Cell re-selection in a cellular telecommunications network

ABSTRACT

According to an aspect of the present disclosure, there may be provided a method in a wireless cellular telecommunications device camped on a serving cell, the device storing a parameter obtained by decoding system information of a first cell. The method comprises: measuring an attribute of a signal received from a candidate cell; and, evaluating the candidate cell for re-selection based on the measured attribute according to a priority-based re-selection algorithm irrespective of the stored parameter. The parameter indicates a minimum required received signal code power. A device and computer readable medium are also provided.

TECHNICAL FIELD

The present disclosure relates to a cellular telecommunications systemand, in particular, to a method of cell re-selection in a mobile devicecamped on a cell of the cellular telecommunications system.

BACKGROUND OF THE INVENTION

In a typical cellular radio system, a wireless telecommunication devicecommunicates via one or more radio access networks (RAN) to one or morecore networks. In a UMTS system such devices are typically referred toas User Equipment (UE) and in a GSM system such devices are typicallyreferred to as Mobile Stations (MS). The terms can be considered asequivalent. In the description herein both terms may be usedinterchangeably, however, it will be noted that the term MS will be usedpredominantly since the present disclosure relates primarily to cellre-selection from a GSM EDGE Radio Access Network (GERAN) to a UMTSTerrestrial Radio Access Network (UTRAN) or an evolved UMTS TerrestrialRadio Access Network (e-UTRAN). It will be clear, however, that thepresent disclosure is not limited to this type of cell re-selection.

The Mobile Station (MS) comprises various types of equipment such asmobile telephones (also known as cellular or cell phones), laptops withwireless communication capability, tablet computers and personal digitalassistants (PDAs) among others. These may be portable, hand held, pocketsized or installed in a vehicle for example and communicate voice ordata signals or both with the radio access network (RAN). Of course theMS may not be mobile, but may be fixed in a location. In this contextthe term mobile may simply refer to the communication capabilities ofthe device.

In the following, reference will be made to Global System for MobileCommunications (GSM), Universal Mobile Telecommunications System (UMTS),Long Term Evolution (LTE) and to particular standards. However it shouldbe understood that the present disclosure is not intended to be limitedto any particular mobile telecommunications system or standard.

The RAN covers a geographical area divided into a plurality of cellareas. Each cell area is served by at least one base station, which inUMTS may be referred to as a Node B or enhanced Node B in LTE. Each cellmay be identified by a unique identifier which is broadcast in the cell.The base stations communicate at radio frequencies over a radiointerface with the UEs which are camped on the cell (these may be someor all of the UEs which are within the range of the base station).Several base stations may be connected to a radio network controller(RNC) which controls various activities of the base stations. The RNCsare typically connected to a core network. Each cell implements aparticular radio access technology (RAT) such as UMTS Terrestrial RadioAccess (UTRA) among others. In a GERAN (Global system for mobilecommunications (GSM)/Enhanced Data rates for GSM Evolution (EDGE) radioaccess network), the radio access network may include one or more basestations (BTSs) and one or more Base station controllers (BSCs) whichtogether implement the functionality of the base station subsystem (BSS)in respect of any particular cell.

Cell selection, sometimes referred to as cell search, for a UE isdescribed in the 3GPP TS 25.304 specification, V8.1.0, “User Equipment(UE) procedures in idle mode and procedures for cell re-selection inconnected mode” which is incorporated herein by reference and referredto herein as the 25.304 specification. Section 5.2.3 and in particularsection 5.2.3.1.1 of the 25.304 specification describes the cellselection process. One of the considerations in the cell selectionprocess is whether a cell is “suitable”. Criteria for suitability mayinclude criteria related to signal strength and/or signal quality(referring to the signal transmitted by the candidate cell base station,as received by the UE). Some of the criteria that are used in thesuitability evaluation are based on parameters which must be decoded bythe device after tuning to the frequency of the candidate cell.

When idle, an MS will evaluate the properties of detectedtelecommunications cells, other than the cell it is currently connectedto or camped on (often known as the serving cell), in order to identifyif the detected or candidate cells would be better suited for connectionrather than the serving cell. The process of the MS autonomouslychanging the serving cell while in idle mode is known as cellre-selection (though re-selection may not be restricted to idle mode orpurely autonomous cell change or both). The process by which an MS firstcamps on a cell following power-up or loss of radio coverage is known ascell selection. The criteria for cell re-selection may include suchthings as received signal strength and signal quality. Parametersassociated with these criteria may be broadcast or otherwise transmittedin the serving cell. One of the requirements for cell re-selection (andselection) may be that the candidate cell is suitable. The criteria forsuitability may include criteria related to signal strength and/orsignal quality (referring to the signal transmitted by the candidatecell base station, as received by the MS). Some of the criteria that areused in the suitability evaluation are based on parameters which must bedecoded by the MS after tuning to the frequency of the candidate cell.The decoding of the parameters from the candidate cell can requiresignificant battery power for the MS. Regular evaluation based ondecoding suitability parameters in this way is particularly undesirablein mobile devices where battery life is limited.

The existing solution to this problem is to store and re-use the mostrecently decoded suitability criteria parameters. This solution isoutlined in the 3GPP TS 45.008 specification V9.4.0, which isincorporated herein by reference and referred to herein as the ‘45.008specification’. Section 6.6.5, section 6.6.6 and section 6.6.7 of the45.008 specification describe the cell re-selection processes, entitled“Algorithm for cell re-selection from GSM to UTRAN”, “Algorithm forinter-RAT cell re-selection based on priority information” and “Cellselection and re-selection to CSG cells and hybrid cells”, respectively.The algorithm defined in Section 6.6.5 may be described as the ‘rankingalgorithm’ and the algorithm defined in Section 6.6.6 may be describedas the ‘priority-based algorithm’. These terms may be used throughoutthe description herein.

According to the existing solution, when evaluating the suitability of acandidate cell, suitability parameters of a cell from which thesuitability parameters were most recently decoded may be used. Thissolution, although it may reduce the battery usage or long term powerrequirements of the MS, carries with it inherent limitations.Specifically, for example, it is easy for an MS to discount thesuitability of candidate cell and thus not re-select to the cell when itshould. This may be because the parameters used to evaluate itssuitability are incorrect, for example because the suitabilityparameters of the candidate cell are not the same as those that arebeing applied. Alternatively, an MS may incorrectly consider a cell as avalid cell for re-selection and proceed to, wastefully, tune to thecandidate cell's frequency and decode parameters from that cell. Thismay be a particular problem if a wide range of threshold parameters areapplicable to the cells that the MS could potentially reselect to. Whenone of these threshold parameters are stored, it may be used toincorrectly evaluate another cell in the network for which a differentvalue is applicable.

In an example scenario, an operator may wish that devices in idle modecamp on cells of one frequency, and devices in connected mode, i.e. withactive ongoing data or voice calls, operate in cells of a differentfrequency. The operator may attempt to achieve this by discouraging idlemode re-selection to a particular frequency by means of the suitabilitycriteria, i.e. the suitability criteria are set such that an MS will bevery unlikely to meet those criteria. In this scenario, the MS mayevaluate such cells for suitability using a considerable amount of powerin the process based on criteria that are easier to meet. Additionally,if the MS has stored these incorrect parameters for re-use in thesuitability evaluation for other cells, the MS may not camp on a cell onwhich it should.

It would be desirable for a candidate cell meeting the re-selectioncriteria to not fail the suitability aspect of the re-selection tests.The present disclosure addresses the problem of how to efficiently andeffectively evaluate a candidate cell for re-selection. The presentdisclosure minimises the need to tune to the frequency of a candidatecell and decode suitability parameters from candidate cells whileavoiding the risk of discounting a candidate cell incorrectly.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present disclosure will now be described in detail withreference to the accompanying drawings, in which:

FIG. 1A is a diagram showing an overview of a network and a UE device;

FIG. 1B shows a schematic system suitable for implementing a firstembodiment of the present invention;

FIG. 2 shows a flow diagram of a known ranking algorithm for cellre-selection;

FIG. 3 shows a flow diagram of a known method of storing suitabilityparameters when performing cell re-selection;

FIG. 4 shows a flow diagram illustrating an example of the presentdisclosure in which stored suitability parameters are applied on aper-frequency basis;

FIG. 5 shows a view of information flow illustrating an example of thepresent disclosure in which stored suitability parameters are applied ona per-frequency basis;

FIG. 6 shows a flow diagram illustrating an example of the presentdisclosure in which stored suitability parameters are applied on aper-cell basis;

FIG. 7 shows a flow diagram illustrating an example of the presentdisclosure relating to Closed Subscriber Group (CSG) Cells;

FIG. 8 shows a flow diagram illustrating an example of the presentdisclosure relating to storage of suitability criteria;

FIG. 9 shows a flow diagram illustrating an example of the presentdisclosure relating to priority-based re-selection;

FIG. 10 shows a process illustrating an example of the presentdisclosure in which stored suitability parameters are applied on aper-frequency basis;

FIG. 11 shows a process illustrating an example of the presentdisclosure in which stored suitability parameters are applied on aper-cell basis;

FIG. 12 shows a process illustrating an example of the presentdisclosure relating to Closed Subscriber Group (CSG) Cells;

FIG. 13 shows a process illustrating an example of the presentdisclosure relating to Closed Subscriber Group (CSG) Cells;

FIG. 14 shows a process illustrating an example of the presentdisclosure relating to Closed Subscriber Group (CSG) Cells;

FIG. 15 shows a process illustrating an example of the presentdisclosure relating to priority-based re-selection; and,

FIG. 16 shows a flow diagram illustrating an example of the presentdisclosure in which certain radio-related evaluations are not performed.

The same reference numerals used in different figures denote similarelements.

DETAILED DESCRIPTION

Embodiments set out in this application relate generally to a method ofcell re-selection in an electronic device. Embodiments may efficientlyevaluate a candidate cell when performing re-selection, without havingto tune to the frequency of a candidate cell and decode suitabilityparameters from that cell every time the evaluation is performed.

According to an aspect of the present invention, there is provided amethod in a wireless cellular telecommunications device camped on aserving cell, the device storing a parameter obtained from a first cell,the method comprising:

measuring an attribute of a signal received from a candidate cell; and,

evaluating the candidate cell for re-selection,

wherein if a carrier frequency of the candidate cell matches a carrierfrequency of the first cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute and the storedparameter, else

the evaluation of the candidate cell for re-selection is performedwithout using the stored parameter.

According to an aspect of the present disclosure, there may be provideda method in a wireless cellular telecommunications device camped on aserving cell, the device storing a parameter obtained from a first cell,the method comprising:

measuring an attribute of a signal received from a candidate UTRAN cell;and,

evaluating the candidate cell for re-selection, wherein, if a carrierfrequency of the candidate cell matches a carrier frequency of the firstcell, the evaluation of the candidate cell for re-selection is based onat least the measured attribute and the stored parameter, else

the evaluation of the candidate cell for re-selection is performedwithout using the stored parameter.

According to an aspect of the present disclosure, there may be provideda method in a wireless cellular telecommunications device camped on aserving cell, the device storing a parameter obtained from a first cell,the method comprising:

measuring an attribute of a signal received from a candidate cell; and,

evaluating the candidate cell for re-selection according to a rankingalgorithm,

wherein, if a carrier frequency of the candidate cell matches a carrierfrequency of the first cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute and the storedparameter, else

the evaluation of the candidate cell for re-selection is performedwithout using the stored parameter. The candidate cell may be a UTRANcell.

In certain embodiments the method may further comprise performingre-selection from the serving cell to the candidate cell based on theevaluation.

Additionally, if the frequency of the candidate cell matches thefrequency of the first cell, the evaluation may also include determiningif the candidate cell meets re-selection requirements, wherein, if themeasured attribute fails to exceed the stored parameter by a firstpre-determined amount, the evaluation includes determining that thecandidate cell does not meet re-selection requirements. The firstpredetermined amount may be +10 dB.

Further, if the carrier frequency of the candidate cell does not matchthe carrier frequency of the first cell, the evaluation of the candidatecell for re-selection may include: determining if the measured attributeexceeds a predetermined default value; and, if the measured attributefails to exceed the predetermined default value, determining that thecandidate cell does not meet re-selection requirements.

Additionally, the first cell may be different from the serving cell, thedevice having been previously camped on the first cell. Alternatively,the first cell and the candidate cell may be of the same wireless radioaccess technology.

In certain embodiments, the evaluation of the candidate cell mayinclude: acquiring system information of the candidate cell, the systeminformation including a parameter; determining if the measured attributeexceeds the candidate cell parameter by a second predetermined amount;and, if the measured attribute exceeds the candidate cell parameter bythe second predetermined amount, performing re-selection to thecandidate cell. The second predetermined amount may be 0 dB.

Further, the stored parameter may indicate a minimum required receivelevel. The measured attribute may be received signal code power (RSCP).Additionally, the serving cell may be a GERAN cell.

In certain embodiments, the method may further comprise: acquiring aparameter of a second cell; and, if a carrier frequency of the secondcell does not match the carrier frequency of the first cell, storingsaid second cell parameter, else if the carrier frequency of the secondcell matches the carrier frequency of the first cell, replacing thestored parameter with the second cell parameter such that whenevaluating a candidate cell for re-selection, if the carrier frequencyof the candidate cell matches the carrier frequency of the second cell,the evaluation of the candidate cell for re-selection is based on atleast the measured attribute and the stored second cell parameter. Ifthe candidate cell has an identifier equivalent to an identifier of thefirst cell, the evaluation of the candidate cell for re-selection may bebased on at least the measured attribute and the stored parameter, elsethe evaluation of the candidate cell for re-selection may be performedwithout using the stored parameter. The identifier may be a primaryscrambling code.

Additionally, the method may further comprise: determining if acandidate cell is a closed subscriber group cell; and, if the candidatecell and the first cell are closed subscriber group cells, theevaluation of the candidate cell for re-selection is based on at leastthe measured attribute and the stored parameter, else the evaluation ofthe candidate cell for re-selection is performed without using thestored parameter.

The serving and candidate cells may be of the same wireless radionetwork. Alternatively, the serving and candidate cells may be ofdifferent wireless radio networks.

According to an aspect of the present disclosure, there may be provideda wireless cellular telecommunications device adapted to: camp on aserving cell; store a parameter obtained from a first cell; measure anattribute of a signal received from a candidate UTRAN cell; and,evaluate the candidate cell for re-selection, wherein if a carrierfrequency of the candidate cell matches a carrier frequency of the firstcell, the evaluation of the candidate cell for re-selection is based onat least the measured attribute and the stored parameter, else theevaluation of the candidate cell for re-selection is performed withoutusing the stored parameter.

According to an aspect of the present disclosure, there may be provideda wireless cellular telecommunications device adapted to: camp on aserving cell; store a parameter obtained from a first cell; measure anattribute of a signal received from a candidate cell; and, evaluate thecandidate cell for re-selection according to a ranking algorithm,wherein if a carrier frequency of the candidate cell matches a carrierfrequency of the first cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute and the storedparameter, else the evaluation of the candidate cell for re-selection isperformed without using the stored parameter.

According to an aspect of the present disclosure, there may be provideda computer-readable storage medium having stored thereon instructionswhich can be executed by a device to: camp on a serving cell; store aparameter obtained from a first cell; measure an attribute of a signalreceived from a candidate UTRAN cell; and, evaluate the candidate cellfor re-selection, wherein if a carrier frequency of the candidate cellmatches a carrier frequency of the first cell, the evaluation of thecandidate cell for re-selection is based on at least the measuredattribute and the stored parameter, else the evaluation of the candidatecell for re-selection is performed without using the stored parameter.

According to an aspect of the present disclosure, there may be provideda computer-readable storage medium having stored thereon instructionswhich can be executed by a device to: camp on a serving cell; store aparameter obtained from a first cell; measure an attribute of a signalreceived from a candidate cell; and, evaluate the candidate cell forre-selection according to a ranking algorithm, wherein if a carrierfrequency of the candidate cell matches a carrier frequency of the firstcell, the evaluation of the candidate cell for re-selection is based onat least the measured attribute and the stored parameter, else theevaluation of the candidate cell for re-selection is performed withoutusing the stored parameter.

According to an aspect of the present disclosure, there may be provideda method in a wireless cellular telecommunications device camped on aserving cell, the device storing a parameter obtained from a first cell,the method comprising:

measuring an attribute of a signal received from a candidate cell; and,

evaluating the candidate cell for re-selection,

wherein, if the candidate cell has an identifier equivalent to anidentifier of the first cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute and the storedparameter, else the evaluation of the candidate cell for re-selection isperformed without using the stored parameter.

In certain embodiments, if the candidate cell has an identifierequivalent to the identifier of the first cell, the evaluation mayinclude determining if the candidate cell meets re-selectionrequirements, wherein, if the measured attribute fails to exceed thestored parameter by a first pre-determined amount, the evaluationincludes determining that the candidate cell does not meet re-selectionrequirements. The first predetermined amount may be 0 dB. Alternatively,the first predetermined amount may be +10 dB.

According to an aspect of the present disclosure, there may be provideda method in a wireless cellular telecommunications device camped on aserving cell, the device storing a first parameter obtained from systeminformation of a first cell, the method comprising:

measuring an attribute of a signal received from a candidate cell;

determining if the candidate cell is a closed subscriber group cell;and,

evaluating the candidate cell for re-selection,

wherein, if the candidate cell is determined to be a closed subscribergroup cell, the evaluation of the candidate cell for re-selection isbased on at least the measured attribute irrespective of the firststored parameter, said first stored parameter indicating a minimum valuefor the measured attribute.

In certain embodiments, the device has a second stored parameterobtained from a closed subscriber group cell and in which the first cellis not a closed subscriber group cell, wherein, if the candidate cell isdetermined to be a closed subscriber group cell, the evaluation of thecandidate cell for re-selection is based on at least the measuredattribute and the second stored parameter.

Additionally, if the evaluation is based on at least the measuredattribute and the second stored parameter, the evaluation may includedetermining if the cell meets re-selection requirements, wherein, if themeasured attribute fails to exceed the second stored parameter by afirst pre-determined amount, determining that the candidate cell doesnot to meet re-selection requirements. The first predetermined amountmay be 0 dB. Alternatively, the first predetermined amount may be +10dB.

Further, if the candidate cell has an identifier equivalent to anidentifier of the second cell and the candidate cell is determined to bea closed subscriber group cell, the evaluation of the candidate cell forre-selection may be based on at least the second stored parameter, elsethe evaluation of the candidate cell for re-selection is performedwithout using the second stored parameter.

The identifier may be a locally unique identifier. The identifier may bea physical layer identifier. The identifier may be a primary scramblingcode.

In certain embodiments, if the candidate cell has a carrier frequencymatching a carrier frequency of the second cell and the candidate cellhas a primary scrambling code matching the primary scrambling code ofthe second cell and the candidate cell is determined to be a closedsubscriber group cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute and secondstored parameter, else the evaluation of the candidate cell forre-selection is performed without using the second stored parameter.

Additionally, if the evaluation is performed without using the storedparameter, the evaluation of the candidate cell may include: determiningif the measured attribute exceeds a predetermined default value; and, ifthe measured attribute fails to exceed the predetermined default value,determining that the candidate cell does not meet re-selectionrequirements.

The candidate cell may be a UTRAN cell. The candidate cell may be aE-UTRAN cell. The identifier of the first cell may also be a physicallayer cell identifier. The serving cell may be a GERAN cell.

In certain embodiments, the method may further comprise performingre-selection from the serving cell to the candidate cell based on theevaluation. The evaluation of the candidate cell may also include:acquiring system information of the candidate cell, the systeminformation including a parameter; determining if the measured attributeexceeds the candidate cell parameter by a second predetermined amount;and, if the measured attribute exceeds the candidate cell parameter bythe second predetermined amount, performing re-selection to thecandidate cell. The second predetermined amount may be 0 dB.

Further, the stored parameter may indicate a minimum required receivelevel. The measured attribute may be a received signal code power(RSCP).

Also, the serving and candidate cells, may be of the same wireless radionetwork. Alternatively, the serving and candidate cells may be ofdifferent wireless radio networks.

According to an aspect of the present disclosure, there may be provideda wireless cellular telecommunications device adapted to: camp on aserving cell; store a parameter obtained from a first cell; measure anattribute of a signal received from a candidate cell; and, evaluate thecandidate cell for re-selection, wherein, if the candidate cell has anidentifier equivalent to an identifier of the first cell, the evaluationof the candidate cell for re-selection is based on at least the measuredattribute and the stored parameter, else the evaluation of the candidatecell for re-selection is performed without using the stored parameter.

According to an aspect of the present disclosure, there may be provideda wireless cellular telecommunications device adapted to: camp on aserving cell; store a parameter obtained from system information of afirst cell; measure an attribute of a signal received from a candidatecell; determine if the candidate cell is a closed subscriber group cell;and, evaluate the candidate cell for re-selection, wherein, if thecandidate cell is determined to be a closed subscriber group cell, theevaluation of the candidate cell for re-selection is based on at leastthe measured attribute irrespective of the first stored parameter, theparameter indicating a minimum value for the measured attribute.

According to an aspect of the present disclosure, there may be provideda computer-readable storage medium having stored thereon instructionswhich can be executed by a device to: camp on a serving cell; store aparameter obtained from a first cell; measure an attribute of a signalreceived from a candidate cell; and, evaluate the candidate cell forre-selection, wherein, if the candidate cell has an identifierequivalent to an identifier of the first cell, the evaluation of thecandidate cell for re-selection is based on at least the measuredattribute and the stored parameter, else the evaluation of the candidatecell for re-selection is performed without using the stored parameter.

According to an aspect of the present disclosure, there may be providedA computer-readable storage medium having stored thereon instructionswhich can be executed by a device to: camp on a serving cell; store aparameter obtained from a first cell; measure an attribute of a signalreceived from a candidate cell; determine if the candidate cell is aclosed subscriber group cell; and, evaluate the candidate cell forre-selection, wherein, if the candidate cell is determined to be aclosed subscriber group cell, the evaluation of the candidate cell forre-selection is based on at least the measured attribute irrespective ofthe first stored parameter, the parameter indicating a minimum value forthe measured attribute.

According to an aspect of the present disclosure, there may be provideda method in a wireless cellular telecommunications device camped on aserving cell, the device storing a parameter obtained by decoding systeminformation of a first cell, the method comprising:

measuring an attribute of a signal received from a candidate cell; and,

evaluating the candidate cell for re-selection based on the measuredattribute according to a priority-based re-selection algorithmirrespective of the stored parameter, wherein the parameter indicates aminimum required received signal code power.

In certain embodiments, the method may further comprise performingre-selection from the serving cell to the candidate cell based on theevaluation. The evaluation of the candidate cell may also includesacquiring system information of the candidate cell, the systeminformation including a parameter; determining if the measured attributeexceeds the candidate cell parameter by a predetermined amount; and, ifthe measured attribute exceeds the candidate cell parameter by apredetermined amount, performing re-selection to the candidate cell. Thepredetermined amount may be 0 dB.

Additionally, the evaluation of the candidate cell for re-selection mayinclude: determining if the measured attribute exceeds a predetermineddefault value; and, if the measured attribute fails to exceed thepredetermined default value, determining that the candidate cell doesnot meet re-selection requirements.

In certain embodiments, the measured attribute may be received signalcode power (RSCP). The candidate cell may be a UTRAN cell. The servingcell may be a GERAN cell.

Further, the method may also comprise: measuring an attribute of asignal received from a second cell; and, evaluating the second cell forre-selection based on the measured attribute and the stored parameteraccording to a ranking algorithm.

Additionally, the serving and candidate cells may be of the samewireless radio network. Alternatively, the serving and candidate cellsmay be of different wireless radio networks.

According to an aspect of the present disclosure, there may be provideda wireless cellular telecommunications device adapted to: camp on aserving cell; store a parameter obtained by decoding system informationof a first cell; measure an attribute of a signal received from acandidate cell; and, evaluate the candidate cell for re-selection basedon the measured attribute according to a priority-based re-selectionalgorithm irrespective of the stored parameter, wherein the parameterindicates a minimum required signal code power.

According to an aspect of the present disclosure, there may be provideda computer-readable storage medium having stored thereon instructionswhich can be executed by a device to: camp on a serving cell; store aparameter obtained by decoding system information of a first cell;measure an attribute of a signal received from a candidate cell; and,evaluate the candidate cell for re-selection based on the measuredattribute according to a priority-based re-selection algorithmirrespective of the stored parameter, wherein the parameter indicates aminimum required signal code power.

Other aspects and features of the present teaching will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of a method and apparatus for cellre-selection in a telecommunication system and the accompanying claims.Any method disclosed herein may be implemented in a mobile stationdevice of a wireless communications network.

Radio Access Networks of the GSM/EDGE (GSM/EDGE Radio Access Network,GERAN), UMTS (UMTS Terrestrial Radio Access Network, UTRAN) or LTE(evolved UMTS Terrestrial Radio Access Network, e-UTRAN) type typicallyinclude multiple cells covering a geographical area each of which mayimplement a different radio access technology (RAT). 2G may refer to GSMand 3G may refer to UMTS and the terms may be used interchangeably. Asdescribed above, a Mobile Station (MS) once connected to a cell, knownas the serving cell, may evaluate other detected cells, known ascandidate cells, to determine if they would be more suitable forconnection than the serving cell. When operating in a cell, the MS isreferred to as being camped on the cell. In the description herein theMS may be referred to as being “in a cell”, “camped on a cell” or usinga “serving cell”. These terms may be used interchangeably and definethat the MS is able to be paged for downlink data by that cell. Thedescription herein may refer to 2G and 3G.

By the terms ‘Ranking Algorithm’ and ‘Priority-Based Re-selectionAlgorithm’ which are used throughout the description herein, we mean thefollowing:

In a ranking algorithm, radio measurements of cells (possibly modifiedby offsets and/or scaling factors, and possibly subject to minimumthresholds) are compared and re-selection is generally made to thehighest thus-ranked cell. In a ranking algorithm, cells on differentfrequencies, or using different radio access technologies may becompared directly and thus ranked relative to each other. Radiomeasurements (or derived values for example based on a received cellsignal quality or power) are the key basis of comparison of candidatecells. An example of a ranking algorithm is shown in FIG. 2.

In a priority-based re-selection algorithm, cells (typically groupedaccording to their frequency of operation and/or radio accesstechnology) are assigned priorities. These priorities are the primarymeans by which cells are considered (radio measurements of the neighbourcells being a secondary consideration) when determining which cell, ifany, the device should reselect to. (Note that other considerations maybe made, such as based on measurements of the serving cell, in additionto the priority level). According to current 3GPP priority-basedre-selection, priorities are assigned on a per-frequency basis (i.e.such that all cells operating using the same radio access technology andsame carrier frequency are assigned the same priority), or (in the caseof GSM cells) on a per-radio access technology (cells operatingaccording to GSM-based technologies operating on different carrierfrequencies may be assigned the same priority). In particular, radiomeasurements of cells of different priorities need not be compared toeach other (though radio measurements may be used for any cell,regardless of its respective priority, to check if it meets minimumcamping/service criteria or to evaluate it against a measurementthreshold). For example, a cell of one priority can be determined tomeet all applicable re-selection criteria, without consideration of anyradio measurements of a cell of a lower priority.

Referring to the drawings, FIG. 1A is a schematic diagram showing anoverview of a UMTS network and a user equipment device. Clearly inpractice there may be many user equipment devices operating with thenetwork but for the sake of simplicity FIG. 1A only shows a single userequipment device 100.

For the purposes of illustration, FIG. 1A also shows a radio accessnetwork 119 (UTRAN) used in a UMTS system having a few components. Itwill be clear to a person skilled in the art that in practice a networkwill include far more components than those shown.

The network 119 as shown in FIG. 1A comprises three Radio NetworkSubsystems (RNS) 102. Each RNS has a Radio Network Controller (RNC) 104.Each RNS 102 has one or more Node B 102 which are similar in function toa Base Transmitter Station of a GSM radio access network. User EquipmentUE 100 may be mobile within the radio access network. Radio connections(indicated by the straight dotted lines in FIG. 1A) are establishedbetween the UE and one or more of the Node Bs in the UTRAN.

FIG. 1B shows a further schematic of a network system. Typically eachradio access network (RAN) includes radio access devices 156 to providethe radio link between the wireless communications device, the MS 160,and the rest of the radio access network. These radio access devices 156are known as base stations in GSM and Node Bs in UMTS. The RAN ine-UTRAN comprises only e-Node Bs. In GSM and UMTS, the RAN alsocomprises a Radio Network Controller (RNC) or Base Station Controller(BSC), 152, 154, and the base stations; the RNCs and BSCs are connectedto one or more core networks (typically at least one for packet-switchedservices and one for circuit-switched services). RNCs connect to 3G basestations (node Bs) and BSCs connect to 2G base stations (in which casethe combined BSC and base station perform the functionality of a basestation subsystem (BSS)), even though they may be physically co-locatedor even in the same unit. The core network (not shown) is associatedwith a Public Land Mobile Network (PLMN) 150; it is possible for asingle RAN to connect to the core networks of multiple PLMNs (notshown).

Each 3G cell may be uniquely (within the local area) identified by afrequency and a primary scrambling code. Generally a cell refers to aradio network object that can be uniquely identified by an MS 160 from acell identifier that is broadcast over geographical areas by a basestation, node B, e Node B or similar entity. A single physical Node Bmay generate more than one cell since it may operate at multiplefrequencies, or with multiple scrambling codes or both. A candidate cellmay be ultimately connected to the same PLMN as the serving cell.

FIG. 2 shows a flow diagram illustrating known processes performed by anMS during a known cell re-selection procedure according to a rankingalgorithm. Referring to FIG. 2, the process starts at step 201. At step202, cell measurements, for example intra-frequency, inter-frequency andinter-RAT cell measurements, are generated or received by the MS. Atstep 203 rank values are calculated for each cell. In one example thesecells are the serving cell and neighbouring cells. One example of thecalculation usable to calculate a rank value in the form of cell-rankingcriterion R is defined in section 5.2.6.1.4 of the 3GPP TS 25.304specification, V8.1.0, “User Equipment (UE) procedures in idle mode andprocedures for cell re-selection in connected mode” which isincorporated herein by reference and referred to herein as the 25.304specification (see the calculations for R, for serving cells and R, forneighbouring cells in that section). In that example the rank values arecalculated for cells if they satisfy the conditions set in section5.2.6.1.4 of the 25.304 specification.

At step 204 the cells are ordered based on the rank values. In oneexample, only cells with rank values better than that of the servingcell are considered and these are compiled in a list. At step 205 theresulting Cell Ranking List is created. At step 206 if the MS finds thatthe serving cell is best (i.e. has the highest rank value) then the MSremains camped on to the serving cell and the process reverts to step202.

If at step 206 the MS finds that the serving cell is not the best (i.e.does not have the highest rank value) then at step 207 the MS attemptsto reselect to a neighbour cell with the highest rank value. To thisend, at 208 a channel (in one example a Primary Common Control PhysicalChannel (PCCPCH)) is set up, at 209 system information (in one examplein the form of Master Information Blocks (MIBs) and System InformationBlocks (SIBs)) is read from the neighbour cell and at 210 a check ismade that the cell is a suitable cell. A suitable cell is a cell onwhich an MS may camp; examples include a cell which has acceptablesignal strength and/or is not in a forbidden location area and/or is notbarred and/or for an automatic search, belongs to the correct PublicLand Mobile Network (PLMN). If the cell is suitable the MS camps on tothe neighbour cell at 211. If the cell is not a suitable cell, theprocess reverts to 202. The process ends at 212.

As noted above, the process shown in FIG. 2 requires that acommunications channel is established with the candidate cell in orderto determine the system information from the cell and hence thesuitability of the cell for selection. Generally, the described processof establishing a channel with the candidate cell is simply to permitthe decoding of system information, which is broadcast. In the contextof the present disclosure, establishing a communications channel doesnot, necessarily, imply any particular behaviour by the network, thatis, the network does not positively ‘establish’ the channel, given thatit may continually broadcast the system information.

This decoding is particularly power intensive and time-consuming for theMS. If the serving cell is a GERAN cell, then it is likely that it willoften be below a neighbouring cell in the ranking list as a result ofthe ranking calculation. Consequently the MS may be repeatedly bechecking the neighbouring cells for suitability and thereforeestablishing communication channels on those cells to decode the systeminformation.

It may be the case that the system information received from theneighbouring cells contains a parameter of suitability such that it isunlikely that the MS will ever determine that cell to be suitable. Theparameter may have been set by the network operator so that MS can varyrarely, if ever, camp on that cell. In this scenario, the MS willrepeatedly establish a communication channel on the cell using a largeand unnecessary amount of power in the process.

In an example scenario, an operator may wish that devices in idle modecamp on cells of one frequency, and devices in connected mode, i.e. withactive ongoing data or voice calls, operate in cells of a differentfrequency. The operator may attempt to achieve this by discouraging idlemode re-selection to a particular frequency by means of the suitabilitycriteria, i.e. the suitability criteria are set such that an MS will bevery unlikely to meet those criteria. In the scenario above, the MS willconsistently evaluate such a cell for suitability using a considerableamount of power in the process, even though the cell may never besuitable.

It has previously been proposed that, in order to reduce the powerrequirements of the MS, it may store previously decoded suitabilityparameters. The reason for requiring storage of suitability criteria isto allow the MS to evaluate a candidate cell, using these criteria,without having to first read the SIBs of the candidate cell (which wouldotherwise have to be read in order to determine the suitability criteriaapplicable to that cell). In many cases, the cell will not meet thesuitability criteria (based on the stored parameters) and no furtherevaluation of this cell is needed; thus, storing criteria from aprevious attempt can significantly reduce the battery consumption asSIBs need not be read from cells which do not meet these criteria.

However, such storage may cause problems if the networks are configuredas described above, particularly if the stored parameters are associatedwith (i.e. decoded from) a cell where idle mode re-selection is intendedto be restricted, i.e. those with unachievable (or rarely achievable)parameters. Since the stored suitability criteria are unlikely to bemet, the MS will not attempt re-selection (noting that the MS mayabandon re-selection at this stage, without reading the systeminformation of the target cell and therefore without being able todetermine that, in actual fact, the suitability criteria would be metfor this cell). In certain circumstances, the MS could remain camped ona GSM cell longer than intended in instances where a UMTS cell would bemore appropriate.

The suitability parameters or threshold criteria, may indicate a minimumrequired receive level. The signal quality, signal power or signalstrength of the cell may need to exceed this by a predetermined amount,for example 0 dB or +10 dB. The suitability parameters or thresholdcriteria may, in practice, be the Qrxlevmin value or the Pcompensationvalue or both. Other suitability parameters or threshold criteria are ofcourse considered.

The stored Qrxlevmin value may have a range of −115 to −24 dBm, andthere is no default value (a value to be used if value not explicitlysignalled), since its inclusion in the 3G cell's system information ismandatory. Qrxlevmin may be a suitability parameter for that cell.

Pcompensation is a further suitability parameter derived (at leastpartly) from one or more parameters broadcast in the cell also currentlyreferred to in Section 6.6.5 of the 45.008 specification. Its value ismost likely to be 0 dB.

FIG. 3 illustrates the known process of cell re-selection using storedparameters. The algorithm applicable is outlined in the 45.008specification. Specifically, section 6.6.5, entitled “Algorithm for cellre-selection from GSM to UTRAN”.

The illustrated process starts at step 302 with the MS camped on theserving cell. Depending on the configuration and the algorithm used, theneighbour cell is received from the serving cell (step 304) and there-selection parameters are decoded from that list (step 306). The MSthen identifies a candidate cell and performs measurements (step 308).These may include signal strength and signal quality among others. Next,at step 310, the MS determines if the candidate cell meets there-selection criteria. This test may be limited to those criteria whichcan be derived from parameters received in the serving cell. In somecases, depending on the parameters broadcast in the serving cell andwhether or not it has stored suitability parameters, the MS may omitevaluating the candidate cell based on stored suitability parameters. Ifthe candidate cell does not meet the re-selection criteria, the processrestarts as the cell is not acceptable (step 312).

Between steps 312 and 314 (not shown), if the serving cell transmitsReceived Signal Code Power (RSCP) parameters to be used in lieu of the‘suitability test’ within the re-selection algorithm, then the candidatecell is evaluated against these regardless of whether it has storedsuitability parameters or not. If this test is done and passed (notshown), the process moves to step 318.

If the candidate cell is acceptable, the MS checks if it has storedsuitability parameters from a previous attempt (step 314). If it does,the candidate cell is evaluated to determine if it meets suitabilitycriteria based on these stored parameters (step 316). If the candidatecell does not meet the suitability criteria, the cell is deemedunacceptable and the process is restarted (step 312). If the cell doesmeet the suitability criteria based on the stored parameters, then theMS establishes a communication channel with the cell and acquires systeminformation from the candidate cell (step 318). Similarly, if the MSdoes not have stored suitability parameters from a previous attempt, theMS establishes a communication channel with the cell and acquires systeminformation from the candidate cell (step 318).

The suitability of the cell is then evaluated using parameters in thesystem information (step 320). If the candidate cell meets thesuitability criteria, the MS camps on the cell (step 324). If thecandidate cell does not meet the suitability requirements, the cell isdeemed not acceptable (step 312) and the MS remains camped on theserving cell.

Section 6.6.5, “Algorithm for cell re-selection from GSM to UTRAN”,outlines the algorithm for determining the re-selection suitabilitydescribed above and based on a ranking algorithm. The ranking algorithmis used where priority based re-selection is not, for example, due tonetwork configuration or device capability. Section 6.6.6, entitled“Algorithm for inter-RAT cell re-selection based on priorityinformation” outlines the priority-based re-selection. Typically,priority-based re-selection is preferred. For example, a device which iscapable of LTE must support priority-based re-selection. In the rankingalgorithm, criteria for re-selection from GERAN to UTRAN may be referredto as CPICH RSCP-based criteria. CPICH stands for common pilot channeland RSCP stands for Received Signal Code Power. For reference, anexcerpt of the algorithm defined in section 6.6.5 of the 45.008specification is as follows, where FDD stands for Frequency DivisionDuplex and MS for Mobile Station:

“If the 3G Cell Re-selection list includes UTRAN frequencies, the MSshall, at least every 5s update the value RLA_C for the serving cell andeach of the at least 6 strongest non-serving GSM cells.

The MS shall then reselect a suitable (see TS 25.304) UTRAN cell if:

-   -   for a TDD cell the measured RSCP value exceeds the value of        RLA_C    -   for the serving cell and all of the suitable (see 3GPP TS 03.22)        non-serving GSM cells by the value XXX_Qoffset for a period of 5        s and    -   for an FDD cell the following criteria are all met for a period        of 5 s:        -   1. its measured RSCP value exceeds the value of RLA_C for            the serving cell and all of the suitable (see 3GPP TS 03.22)            non-serving GSM cells by the value XXX_Qoffset,        -   2. its measured Ec/No value is equal or greater than the            value FDD_Qmin, and

3. its measured RSCP value is equal to or greater thanFDD_RSCP_threshold, if supported by the MS.

In case of a cell re-selection occurring within the previous 15 seconds,XXX_Qoffset is increased by 5 dB where

-   -   FDD_RSCP_threshold equals Qrxlevmin+Pcompensation+10 dB, if        these parameters are available, otherwise−∞ (criterion not        effective).    -   Qrxlevmin is the minimum required RX level in the UTRAN FDD cell        (dBm), see 3GPP TS 25.304.    -   Pcompensation is max(UE_TXPWR_MAX_RACH−P_MAX, 0) (dB), see 3GPP        TS 25.304.    -   UE_TXPWR_MAX_RACH is the maximum TX power level an MS may use        when accessing the UTRAN FDD cell on RACH (dBm), see 3GPP TS        25.304.    -   P_MAX is the maximum RF output power of the MS (dBm) in UTRAN        FDD mode, see 3GPP TS 25.304.    -   FDD_Qmin and XXX_Qoffset are broadcast on BCCH of the serving        cell. XXX indicates other radio access technology/mode.

Note: The parameters required to determine if the UTRAN cell is suitableare broadcast on BCCH of the UTRAN cell. An MS may start re-selectiontowards the UTRAN cell before decoding the BCCH of the UTRAN cell,leading to a short interruption of service if the UTRAN cell is notsuitable.

The MS may store the UTRAN cell RSCP suitability criterion parametersabove, whenever decoded from a UTRAN FDD cell of an equivalent PLMN. Themost recently decoded parameters are valid re-selection criteria towardsall UTRAN FDD cells. This list of parameters shall be cleared after PLMNselection (see 3GPP TS 23.122).”

It should be noted that the definition of suitable in the abovealgorithm requires that cell selection criteria be met. These criteriafor UMTS cells are defined in the 3GPP TS 25.304 specificationsub-clause 5.2.3.1.2. The suitability parameters referred to in the45.008 specification when defining re-selection are Qrxlevmin andPcompensation (which depends on UE_TXPWR_MAX_RACH). The 25.304specification defines other parameters affecting suitability that arenot used in the re-selection tests defined in the 45.008 specification.

For later releases of the specification, the phrase “if supported by theMS” in item 3 above was removed, making this consideration mandatory formobile stations complying with later releases of the specifications.

The definition of FDD_RSCP_threshold has also been previously modifiedto read as follows:

-   -   “FDD_RSCP_threshold equals FDD_RSCPmin−min((P_MAX−21 dBm), 3 dB)        if FDD_RSCPmin is broadcast on the serving cell, else        Qrxlevmin+Pcompensation+10 dB, if these parameters are        available, otherwise the default value of FDD_RSCPmin.”

Additionally, the paragraph starting “The MS may store” of the algorithmwas updated to read as follows:

“The MS shall store the UTRAN cell RSCP suitability criterion parametersabove, whenever decoded from a UTRAN FDD cell of an equivalent PLMNwhile attempting to camp on the UTRAN FDD cell. The most recentlydecoded parameters from one UTRAN FDD cell of an equivalent PLMN arevalid re-selection criteria towards all UTRAN FDD cells. This list ofparameters shall be cleared after PLMN selection (see 3GPP TS 23.122).”

This change was made for the following reasons:

“If the FDD_RSCPmin parameters are not provided in the broadcast of theGSM serving cell, the FDD_RSCP_threshold is derived from broadcastinformation of the UTRAN cells. These parameters could be different foreach UTRAN cell.

It is unclear from which UTRAN cell and when the MS shall read theseparameters and when they should be re-read. Furthermore it is unclearwhether a parameter set of one UTRAN cell is valid for the re-selectiontowards all cells or only towards the UTRAN cell from which theparameters were read.”

When this change to the specification was made, a summary was given asfollows:

“It is clarified that the MS shall refresh the parameter set whenattempting to camp on a UTRAN FDD cell of an equivalent PLMN and thus isnot required to read this parameter from the UTRAN neighbour cells whilecamping on a GSM cell.

It is further clarified, that the parameters received from one UTRANcells are valid re-selection criteria towards all UTRAN FDD cells.”

As stated previously, the reason for requiring storage of suitabilitycriteria is to allow the MS to evaluate a candidate cell, using thesecriteria, without having to first read the System Information Blocks(SIBs) of the candidate cell (which would otherwise have to be read inorder to determine the suitability criteria applicable to that cell). Inmany cases, the cell will not meet the criteria and no furtherevaluation of this cell is needed; thus, storing criteria from aprevious attempt can significantly reduce the battery consumption asSIBs need not be read from cells which do not meet these criteria.

It was mentioned above that Section 6.6.5 applies only where prioritybased re-selection does not. Specifically, Section 6.6.5 states: “Thealgorithm in this subclause shall be used for re-selection from GSM toUTRAN if the conditions for the use of the cell re-selection algorithmbased on priority information (see subclause 6.6.6) are not satisfied”.Section 6.6.6, “Algorithm for inter-RAT cell re-selection based onpriority information”, defines that priority-based re-selection criteriaallow an operator to configure a set of cells (on the same frequency andusing the same RAT) as having a particular priority; differentpriorities can be assigned to different RATs or frequencies or both.Multiple frequencies of the same RAT may share a priority level. Twofrequencies cannot share a priority level if they are used for differentRATs. As with the algorithm defined in section 6.6.5 and discussedabove, there is a requirement that the target or candidate cell besuitable as defined in the 25.304 specification and described above. Forreference, an excerpt of the algorithm defined in section 6.6.6 of the45.008 specification is as follows:

“The MS shall then reselect a suitable (see 3GPP TS 25.304 for UTRAN and3GPP TS 36.304 for E-UTRAN) cell of another radio access technology ifthe criteria below are satisfied. S_non-serving_XXX is the measurementquantity of a non-serving inter-RAT cell and XXX indicates the otherradio access technology/mode and is defined as follows:

-   -   for a UTRAN cell, is the measured RSCP value for the cell minus        UTRAN_Qrxlevmin for the cell's frequency;    -   for a E-UTRAN cell, is the measured RSRP value for the cell        minus E-UTRAN_Qrxlevmin for the cell's frequency if        THRESH_E-UTRAN_high_Q is not provided; otherwise, if        THRESH_E-UTRAN_high_Q is provided, is the measured RSRQ value        for the cell minus E-UTRAN_QQUALMIN for the cell's frequency.        ( . . . )

Cell re-selection to a cell of another inter-RAT frequency shall beperformed if any of the conditions below (to be evaluated in the ordershown) is satisfied:

-   -   The S_non-serving_XXX of one or more cells of a higher priority        inter-RAT frequency is greater than THRESH_XXX_high (or, in case        of an E-UTRAN target, THRESH_E-UTRAN_high_Q, if provided) during        a time interval T_re-selection; in that case, the mobile station        shall consider the cells for re-selection in decreasing order of        priority and, for cells of the same inter-RAT frequency or of        inter-RAT frequencies of equal priority, in decreasing order of        S_non-serving_XXX and reselect the first cell that satisfies the        conditions above;    -   the value of S_GSM is lower than THRESH_GSM_low for the serving        cell and all measured GSM cells during a time interval        T_re-selection; in this case, the mobile station shall consider        for re-selection the inter-RAT cells in the following order, and        reselect the first one that satisfies the following criteria:    -   cells of a lower priority inter-RAT frequency whose        S_non-serving_XXX is greater than THRESH_XXX_low (or, in case of        an E-UTRAN target, THRESH_E-UTRAN_low_Q, if provided) during a        time interval T_re-selection; these cells shall be considered in        decreasing order of priority and, for cells of the same RAT, in        decreasing order of S_non-serving_XXX;    -   if no cells satisfy the criterion above, inter-RAT cells for        which, during a time interval T_re-selection, S_non-serving_XXX        is higher than S_GSM for the serving cell by at least a specific        hysteresis H_PRIO; these cells shall be considered in decreasing        order of S_non-serving_XXX

A UTRAN FDD cell shall only be reselected if, in addition to thecriteria above, its measured Ec/No value is equal to or greater thanFDD_Qmin−FDD_Qmin_Offset.

If E-UTRAN_Qmin is provided for a E-UTRAN frequency, a E-UTRAN cell onthat frequency shall only be reselected if, in addition to the criteriaabove, its measured RSRQ value is equal to or greater than E-UTRAN_Qmin.

If THRESH_E-UTRAN_high_Q is provided for a E-UTRAN frequency, and ifE-UTRAN_RSRPmin is provided, a E-UTRAN cell on that frequency shall onlybe reselected if, in addition to the criteria above, its measured RSRPvalue is equal to or greater than E-UTRAN_RSRPmin. If E-UTRAN_RSRPmin isnot provided, the default value shall be used.

E-UTRAN cells which are included in the list of not allowed cells shallnot be considered as candidates for cell re-selection. If the strongestcells on a E-UTRAN frequency are included in the list of not allowedcells, the mobile station may reselect the strongest valid cell (seesubclause 8.4.7) on that frequency.

Cell re-selection to a cell of another radio access technology (e.g.UTRAN or E-UTRAN) shall not occur within 5 seconds after the MS hasreselected a GSM cell from an inter-RAT cell if a suitable GSM cell canbe found.

If the mobile station applies either common priorities or individualpriorities received through dedicated signalling and priorities areavailable only for some inter-RAT frequencies, cells belonging tofrequencies for which no priority is available or no threshold isprovided by the serving cell shall not be considered for measurement andfor cell re-selection.

If a mobile station in ‘camped normally’ state (see 3GPP TS 43.022)applies individual priorities received through dedicated signalling andno priority is available for the serving cell, the mobile station shallconsider any GSM cell (including the serving cell) to have lowestpriority (i.e. lower than the eight network configured values).

A mobile station in ‘camped on any cell’ state (see 3GPP TS 43.022)shall ignore individual priorities received through dedicated signallingand shall apply priorities received from the system information of theserving cell while attempting to find a suitable cell. If the mobilestation supports CS voice services, the MS shall avoid reselectingacceptable (but not suitable) E-UTRA cells regardless of the prioritiesprovided in system information.

NOTE 4: If the MS is camping on an acceptable cell, individualpriorities are not discarded until an event leading to their deletionoccurs.”

If a cell supports priority-based re-selection according to section6.6.6 of the 45.008 specification, it will transmit to an MS camped onthe cell a list of its neighbouring cells—the ‘neighbour cell list’(this may identify individual cells, or frequencies on which neighbourcells operate, or both). Along with the list, a System Information Type2quater (SI2quater) message may indicate a parameter applicable to oneor more cells in the list, referred to as UTRAN_Qrxlevmin in the excerptabove. This parameter of the candidate cell, which is broadcast in theserving cell, i.e. the UTRAN_Qrxlevmin, is expected in normal operationto be closely related to the corresponding RSCP_threshold sent by therespective cell(s) as used in the suitability check. As such, thisparameter allows the MS to identify if the cell meets an RSCP-basedcriterion without power intensive decoding and evaluation of systeminformation broadcast by the candidate cell unless that criterion ismet.

However, support for priority-based re-selection remains optional fornon-LTE capable devices. For LTE capable devices priority basedre-selection must be used. Moreover, priority-based re-selection is notsupported in any pre-Release 7 devices. In addition, there is thepossibility that priority-based re-selection is not applicable in theserving cell, for example if the cell is a GERAN cell. It is quitepossible that operators will not upgrade GERAN networks to supportpriority-based re-selection, even when LTE is deployed, especially nearthe edges of LTE coverage. Therefore, while LTE cells or UTRAN cellsmost likely will support priority-based re-selection, overlapping ornearby GSM cells may not. A device supporting priority-basedre-selection is required to use the old 6.6.5 rules, i.e. re-selectionaccording to the ranking algorithm, in such a case. In this scenario theproblems described above are applicable; in that an MS may remain campedon a GSM cell longer than is appropriate when a UMTS or LTE capable cellis available but the MS does not consider it to be suitable or powerintensive system information reception and decoding are required.

The priority-based re-selection (PBR) RSCP_threshold parameter broadcastin the serving cell is optional and is set up in the networkconfiguration. The parameter is likely to be (or correlate with) theminimum required measured RSCP level. Additionally, the PBR parametermay be broadcast as a specific value and associated with one or moreexplicitly signalled frequencies, or may be broadcast as a ‘default’value to be used with cells of frequencies not explicitly signalledtogether with the parameter value. The parameter is applicable only tocells which operate on the same frequency associated with the parameter.The default value only applies to frequencies in the neighbour celllist. An example of a broadcast default parameter is theDEFAULT_UTRAN_QRXLEVMIN parameter encoded within the 3G PriorityParameters Description Struct; an example of an parameter associatedwith explicitly signalled frequencies is the UTRAN_QRXLEVMIN parameterencoded within the Repeated UTRAN Priority Parameters struct (see 3GPPTS 44.018 v.10.3.0). If no parameter is broadcast in the cell, thealgorithm specifies a value to be used, i.e. as the UTRAN_Qrxlevmin. ThePBR parameter may not have been broadcast in the cell due to networkconfiguration or may not have been received fully by the MS.

For the purposes of this discussion, a network comprising three cellsmay be considered, although it will be understood that this is only anexample and more cells implementing a variety of Radio AccessTechnologies (RATs) may be equally utilised with the present disclosure.In the examples described, unless indicated to the contrary, a firstcandidate cell, cell A, is a UTRAN cell. Another cell, cell B, is thecell currently serving the MS and is a GERAN cell. Another cell, cell C,is second candidate cell and is also a UTRAN cell. Although GERAN andUTRAN cells are used in this description, it should be understood thatany RAT can be implemented by each cell, however, for the purposes ofthe disclosure, cells A and C should be implementing the same RAT.

As described, referring to the above nomenclature, when an MS isconnected to, or as it is known, camped on, cell B (the serving cell),the MS may evaluate cells A and C to determine their appropriateness forre-selection.

During GSM to UMTS or LTE cell re-selection, the existing 3GPP TS 45.008section 6.6.5 described above, i.e. re-selection according to a rankingalgorithm, mandates the storage and, in some cases, usage of previouslyreceived suitability requirements for UTRAN FDD cells.

The 45.008 specification refers to “equivalent PLMNs”, which may includethe registered PLMN (generally, these procedures are agnostic to whichPLMN is being considered as long as it is within the list of equivalentPLMNs—PLMNs in this list are “regarded as equivalent to each other forPLMN selection, cell selection/re-selection and handover”; TS 23.122sub-clause 4.4.3). The text goes on to indicate that these values arecleared on PLMN selection; however, re-selection between differentequivalent PLMNs is not considered PLMN selection.

This may lead to a scenario where, for example in national roamingscenarios where two operators' PLMNs are set as equivalent to eachother, suitability criteria from one roaming partner are applied to acell of a second roaming partner (or the home or serving PLMN). The useof equivalent PLMNs is up to the operator(s) to determine and the scopeof these problems is not limited to how or why equivalent PLMNs areused, or whether they are used at all.

More importantly and more generally, there is a potential that ifthreshold criteria for a cell or category of cells (such as thoseoperating at a particular frequency) are different from those foranother cell or category of cells (such as those operating on anotherfrequency, either on the same PLMN or on a different, equivalent PLMN),then the behaviour of the mobile station will vary considerablydepending on stored requirements, which may in turn depend on the mostrecent UTRAN cell from which it received (and stored) the requirements.

More specifically, one could consider an exemplary scenario, where anoperator wishes that devices in idle mode camp on cells of onefrequency, and devices in connected mode (i.e. with active ongoingdata/voice calls) operate in cells of a different frequency. Theoperator may attempt to achieve this by discouraging (to the point ofmaking it practically impossible) idle mode re-selection to a particularfrequency by means of the suitability criteria i.e. the suitabilitycriteria are set such that a mobile will be very unlikely to meet thesecriteria.

According to the existing rules, the UE may store and apply these samecriteria (which it decoded as part of an attempt—most likelyunsuccessful—to reselect to a cell on the first frequency) whenevaluating a UTRAN cell on any frequency, including to cells on thesecond frequency where idle mode re-selection is not intended to berestricted.

Since the stored criteria are very unlikely to be met, the MS will notattempt re-selection (noting that the MS may abandon re-selection atthis stage, without reading the system information of the target celland therefore without being able to determine that, in actual fact, thesuitability criteria would be met for this cell).

This problem could restrict 2G to 3G cell re-selection potentiallycausing the device to be essentially stuck in 2G (or at least, remainthere for longer than intended). In some cases the device can move to 3Gonly either if power is turned off or PLMN re-selection happens (see3GPP TS 23.122).

In the case of priority-based re-selection, considering the exemplarycase where a mobile has stored very stringent criteria from one cell,this may make it inappropriately abandon evaluation of a second cell aspart of the priority-based re-selection, even though all the (correct)criteria to permit re-selection evaluation are available in the servingcell.

In addition to the above scenarios, further issues are created by theuse of Closed Subscriber Group (CSG) cells. Home NodeB (HNB), Home eNB(HeNB) or femtocell are concepts introduced for UMTS and LTE (E-UTRAN)to improve indoor and micro-cell coverage as well as to leveragewireline backhaul to the ‘home’. Note that “femtocell” is widely usedoutside of 3GPP to mean any cell with a very small coverage, andtypically installed in a private premises (either private or corporate).The terms HeNB/HNB are used in 3GPP with specific meanings i.e. that thecell is a Closed Subscriber Group (CSG) cell, or hybrid cell.

An important aspect of HeNB/HNB functionality is the ability to restrictaccess to particular users. For example, to employees of the company onwhose site the H(e)NB is deployed, to customers of a particular coffeeshop chain, or (in the case of H(e)NBs deployed in private homes) toindividuals.

To achieve this functionality, 3GPP has defined the concept of a ClosedSubscriber Group. A CSG cell is one which indicates that it is a CSGcell (by means of 1 bit broadcast in the system information) andbroadcasts a CSG ID (also in system information). A cell can onlyindicate one (or none) CSG IDs, however multiple cells may share a CSGID. A device (UE or MS) may be subscribed to multiple CSGs. Suchsubscriptions may be temporary in nature (e.g. a coffee shop allows acustomer 1 hour's access to its CSG).

CSG cells are a specific category of cells, which may be used as “femto”cells or to provide uncoordinated (i.e. not subject to normal radioplanning as is used for “macro” cells) coverage or both. They may belimited to users with specific subscriptions (e.g. associated with anemployer, school/university, coffee shop etc.)

The term “macro” cell, while not having significance in 3GPPspecifications, is widely used to mean a cell other than a CSG cell andis used accordingly in this description.

A CSG cell may operate using UTRAN or E-UTRAN protocols and radiospecifications, and may operate on the same or a different frequency tonon-CSG cells.

UMTS CSG cells will not be listed in the neighbour cell lists of non-CSGcells; therefore legacy UMTS devices (i.e. Release 7 or earlier) willnot search for such cells. Should such a device attempt to access a CSGcell, its registration attempt will be rejected.

E-UTRAN is specified first in Release 8 and therefore all E-UTRANcapable devices will necessarily be “CSG-aware” devices, even if theyhave no CSG subscription.

Re-selection criteria for these cells are different. It is simplyrequired that the cell is suitable, the strongest on the frequency, andaccessible to the device (e.g. it has a subscription to the cell).

Generally, network operators are keen that devices which have asubscription to a CSG cell camp on that cell in preference to a non-CSGcell. However, the determination by the device to search for CSG cellsis implementation-specific, and may be manually triggered. It isexpected that devices will store some information (such as GPScoordinates, a list of macro cells which are detected) corresponding tothe location of cells which they are able to access and use this tospeed up subsequent accesses—this is referred to as ‘fingerprinting’.

The decision of which target cell to camp on is also dependent on thecell selection and re-selection rule defined for UTRAN and E-UTRAN.Currently, in Release 8, it is specified that a UE may re-select to acell only if it is the best cell (i.e. the cell with the strongestsignal strength) of any cells using its particular carrier frequency. Itis also specified that while the UE is camped on a suitable CSG cell,the UE shall always consider the current frequency to be the highestpriority frequency.

Idle mode re-selection away from CSG cells towards a non-CSG cellfollows legacy behaviour for re-selection to such cells. However, noparameters for cell re-selection to CSG cells are likely to be availablein the serving cell, and therefore there is no hint to the device as towhat the criteria might be (as there is in the case of priority-basedre-selection, as described above). Furthermore, these cells are likelyto be configured to provide very limited coverage, meaning that theirsuitability requirements may be relatively stringent, compared withnon-CSG cells. Storing suitability requirements from CSG cells and usingthem on non-CSG cells (or vice versa) may result in either veryinfrequent re-selection attempts (because the stored criteria are veryhigh), or drained battery life (if cells are incorrectly determined tomeet the suitability requirements prior to reading the systeminformation of the candidate cell). Even amongst CSG cells, differentcells may have very different requirements.

CSG cells may be identifiable as such based on only their physical layeridentities (frequency, physical layer identity, primary scrambling code,etc.)—either because they operate on a dedicated frequency, or becausethe range of physical layer identities is transmitted in the network.

Hybrid cells (introduced in Release 9) are yet a further category ofcells that may have different suitability requirements from non-hybridcells.

In E-UTRAN, neighbour cell lists are not explicit i.e. they do notpositively identify cells: they simply indicate a frequency and,optionally, a list of “Not Allowed” (blacklisted) cells that mobilesshould not attempt to access. Devices are expected to detect cells on afrequency by blind searching. However, this may lead to a significantproblem in the case where many of the detected cells are CSG cells. Inorder to minimize unnecessary processing of such cells by devices whichhave no CSG subscription, the network may optionally indicate the “PCIsplit” applicable to CSG cells, that is, the set of physical layer cellidentities/identifiers that are reserved for CSG cells.

The PSC split is the analagous indication for UMTS cells, in case anoperator does list CSG cells in the neighbour cell list.

There has also been discussion of using a PCI/PSC split to distinguishbetween hybrid cells and non-hybrid cells.

It is worth noting that CSG cells may have significantly differentcriteria for re-selection (compared with other, non-CSG cells, orpossibly even compared to other CSG cells) and that they may beidentifiable as being CSG cells without the need for decoding ofbroadcast system information (e.g. based on physical layer parameters:frequency/PSC/PCI etc.), as is described above.

There currently exists no solution to resolve the problems identifiedand described above.

Example of the Present Disclosure

In accordance with the present disclosure, it is proposed that thresholdcriteria decoded from cells are selectively stored and used in orderthat the evaluation of candidate cells be efficient and more accuratethan present solutions.

It is proposed and described by way of exemplary implementation, thatstorage and usage of stored suitability requirements discriminatesbetween cells (or classes of cells) that can be discriminated at thephysical layer, for example where physical layer addresses (or rangesthereof) and/or operating frequencies are used to distinguish categoriesof cells. In this way, an MS can discriminate stored suitabilityrequirements according to a class of cell or an individual cell withouthaving to establish a communication channel on that cell. In oneexample, requirements are used according to the frequency of the cell orthe identity of the cell. In one example, CSG cells versus non-CSG cellrequirements is an exemplary discrimination (CSG cells are likely to usea dedicated range of physical layer addresses, which may be either PCI(E-UTRAN cells) or PSC (UTRAN cells)). Additionally, usage of storedparameters may be restricted to individual CSG cells (i.e. can only beused in evaluating the same cell as that from which they were received).

Additionally, previously stored suitability requirements (which may havebeen obtained as a result of ranking-based re-selection) shall not beused when evaluating cells according to priority-based re-selectionrules. This may be dependent on whether the corresponding (signalquality/signal strength) parameters are available in the current servingcell. The network may be configured not to send these parameters, i.e.the parameters may not be included in the system information of thecurrent serving cell.

In a first embodiment, threshold criteria are stored and used inaccordance with the frequency of the applicable cell. For example,threshold parameters are stored on the device and linked with thefrequency of the cell from which they were decoded. These parameters arethen only to be used when evaluating cells of that frequency. In thisway, network defined configurations of cells having particularfrequencies are prevented from causing an MS to remain camped on a cellincorrectly. In a further example, for priority-based re-selection,threshold criteria may be stored and re-used on a per-priority levelbasis

As illustrated in FIG. 4, storage and usage of stored suitabilityrequirements may be on a per frequency basis. In other words,requirements decoded from a cell on frequency A are used only forevaluation of other cells on the same frequency.

The illustrated process begins with the MS being camped on a servingcell. In this description, the serving cell may be described as ‘cellB’. The serving cell may be of any RAT, but in this example, it may beconsidered as a GSM cell for convenience. It is irrelevant whether theMS camped on the serving cell by using cell re-selection or cellselection. Optionally, the MS will acquire the UMTS or LTE neighbourcell list. This may be broadcast in the serving cell or may be acquiredotherwise (step 404). The re-selection parameters may be decoded fromthe neighbour cell list (step 406).

Once these optional steps have been performed, the MS may then identifya candidate cell. This may or may not be from the neighbour cell list.The MS then acquires measurements of the identified cell to identifycharacteristics of the cell such as signal strength, signal quality orsignal power (step 408). It will be understood that the steps may becarried out in any particular order. In a specific example, it may beenvisaged that the measurements are performed for all cells in the listbefore a candidate cell is identified.

Once a candidate cell has been identified and measurements of that cellhave been performed, the MS determines if the cell meets initialre-selection requirements (step 410). This test may be based on theparameters decoded from the serving cell in the neighbour cell list. Ifthe cell is deemed not to meet these initial re-selection requirements,then the MS will remain camped on the serving cell and will not continuethe re-selection process.

If the MS determines that the cell meets the initial re-selectioncriteria, then the MS will check if it has any stored criteria relatedto suitability previously decoded from another cell (step 412). Theparameters may have been decoded from the system information of a cellwhen evaluating the cell's suitability. If the MS has criteria stored,the MS will then determine if the criteria is from a cell having thesame frequency as the candidate cell (step 414). The criteria must havebeen decoded from the system information of a cell operating on the samefrequency as the candidate cell. To enable this, the MS may be requiredto maintain an indication of the frequency of the cell the criteria wasdetermined from, in association with the criteria in the data store. Inthis description, the candidate cell may be referred to as ‘cell C’ forconvenience.

If the parameters are determined to be from a cell having the samefrequency as the candidate cell, the candidate cell is checked for itsappropriateness for re-selection (step 416). The stored criteria, from aprevious suitability check, is used to determine if the cell meets theserequirements. In one example, the measurements performed by the MS areused to determine if the cell meets a particular threshold. If thecandidate cell does not meet or exceed the requirements based on thestored parameter, for example the characteristics of a signal receivedby the MS from the cell do not exceed the threshold indicated by theparameter, the process stops and the MS remains camped on the servingcell. It should be noted that the attribute(s) of the signal may have toexceed the threshold by a predetermined amount, which may for example be0 dB or +10 dB. The parameter may be the minimum receive level, theQRXLEVMIN value.

Conventionally, a stored Qrxlevmin value may have a range of −115 to −24dBm, and there is no default value, since its inclusion in the 3G cell'ssystem information is mandatory. Qrxlevmin may be a suitabilityparameter for that cell.

Pcompensation is a further suitability parameter derived (at leastpartly) from one or more parameters broadcast in the cell also currentlyreferred to in Section 6.6.5 of the 45.008 specification. Its value ismost likely to be 0 dB.

If, based on the parameter, it is determined that the candidate cellmeets or exceeds the requirement then the MS may go on to furtherevaluate the cell in the known manner, for example, by tuning to thefrequency of the cell and evaluating it using decoded data. If the MSdoes not have stored criteria available (step 412) or if the MS does nothave stored criteria obtained from a cell having the same frequency asthe candidate cell (step 414), then this decoding is performed.

Optionally, before acquiring the system information of the candidatecell to decode suitability parameters at step 418, not shown is that theMS may evaluate the candidate cell using default parameters which arenot explicitly signalled. In one example the default parameter is apredetermined amount and is specified in the re-selection specification.If the candidate cell does not meet the requirements based on thisdefault parameter, the MS does not continue with the re-selection andthe MS remains camped on the serving cell. If the MS does meet theserequirements based on the default parameter, the MS continues with there-selection process.

In the illustrated example, at step 418, the MS may acquire the systeminformation of the candidate cell. To do this, the MS may establish acommunication channel on the cell and tune to its frequency. The systeminformation may be in the form of a System Information Block (SIB) andmay be obtained by tuning to the frequency of the cell and establishinga communication channel on it. The system information is generic and maybe derived from other blocks than the SIB referred to throughout thepresent disclosure. The MS will then decode the system information toacquire suitability parameters and evaluate the cell based on theseparameters (step 420). If it is determined that the MS meets theserequirements (step 422), for example, based on the measurementspreviously performed in addition to the decoded parameters, the MS maycamp on the candidate cell and perform re-selection to it (step 424). Ifthe MS is deemed to be unsuitable, the MS will remain camped on theserving cell.

Additionally and optionally, a registration update may be performed whenthe MS has camped in the new cell (not shown). This registration updatemay explicitly notify the network that the MS has re-selected to a newcell or new registration area. Additionally and optionally, data may betransmitted and received to and from the network in the new cell (notshown). The registration update step (not shown) may include for examplea routing area update, location update, combined routing area update orsimilar. For further information regarding registration updates pleasesee the 3GPP TS 24.008 specification, “Mobile radio interface Layer 3specification; Core network protocols; Stage 3”, which is incorporatedherein by reference.

FIG. 5 provides a high level view of the information flow. When an MS iscamped on a 3G cell 504, the RSCP suitability criterion parameters arestored according to the frequency of the cell. This store 506 maycontain multiple parameters and frequencies. As shown, when performing2G to 3G cell re-selection, i.e. from cell 502 to cell 504, the storedinformation is used on a per-frequency basis.

In order to effect the above example, it may be advantageous for an MSto maintain a list of frequencies and threshold parameters. For example,for every cell having a new frequency encountered, the thresholdparameters for that frequency are stored. Additionally, each time newthreshold parameters are decoded from a cell having a particularfrequency, the stored criteria can be replaced. This may occur, once theMS has decoded the system information of a cell (step 420) if the cellpreviously met the criteria (step 616).

In another embodiment, instead of being stored and used on aper-frequency basis, each threshold parameter may be used only on aper-cell basis. FIG. 6 illustrates this example. At step 602, the MS iscamped on the serving cell. The MS may first receive a neighbour celllist from the serving cell (step 604). The MS may then decode certainre-selection parameters from the neighbour cell list broadcast by theserving cell (step 606). The MS then identifies a candidate cell andperforms measurements of it, such as signal strength, quality or power(step 608). If the cell does not meet the re-selection requirements, theMS remains camped on the serving cell. If the candidate cell does meetthe re-selection requirements (step 610), the MS goes on to check if ithas any stored criteria available (step 612). If there are no storedcriteria available at all, the MS continues with the re-selectionprocess and tunes to the frequency of the cell to decode systeminformation.

The MS then checks if there any stored criteria available which wereobtained from a cell having the same cell_ID as the candidate cell (step614). If there are no applicable stored criteria, i.e. none wereobtained from a cell having the same cell_ID as the candidate cell, theMS continues with the re-selection process and tunes to the frequency ofthe cell to decode system information.

The cell_ID may be the scrambling code of the cell or may be anotheridentifier of the cell. The cell_ID need not be globally unique but maybe locally unique. The identifier used to differentiate between cells inthis particular example is an identifier that can be derived from thephysical layer, i.e a physical layer identifier, such that the candidatecell can be identified without having to decode system information ofthe cell. Examples of such locally unique identifiers (that can bederived from the physical layer) include the ‘physical layer cellidentifier’ of an E-UTRAN cell and the ‘primary scrambling code’ of aUTRAN cell.

In this way, criteria can only be applied to the cell from which it wasobtained. This obviates the limitations of conventional re-selectionwhere an MS may be ‘stuck’ unnecessarily. Battery life is stillminimised, when compared to the known storage methods and where noparameters are stored, since an MS will not be tune to the frequency ofa cell multiple times to decode the parameters; once is enough for themto be stored and re-used (for example, they may be re-used if themeasurements change).

If the MS has stored criteria obtained from a cell having the samecell_ID as the candidate cell, the candidate cell is checked againstthese criteria (step 616), for example, using the measurements performedin step 608. If the test is successful, the MS continues with there-selection process. If it is not, the MS remains camped on the servingcell.

Optionally, before acquiring the system information of the candidatecell to decode suitability parameters at step 618, not shown is that theMS may evaluate the candidate cell using default parameters which arenot explicitly signalled. In one example the default parameter is apredetermined amount and is specified in the re-selection specification.If the candidate cell does not meet the requirements based on thisdefault parameter, the MS does not continue with the re-selection andthe MS remains camped on the serving cell. If the MS does meet theserequirements based on the default parameter, the MS continues with there-selection process.

The MS will then, if the conditions described above are met or not asthe case may be, tune to the frequency of the candidate cell and acquiresystem information (step 618). The suitability of the cell forre-selection is then evaluated based on parameters decoded from thesystem information (step 620). If the cell meets the suitabilityrequirements (step 622), the MS may camp on the cell (step 624). If itdoes not, the MS may remain camped on the serving cell (step 602). TheMS may maintain a cell-parameter list, such that for each cell_ID, thelatest parameters decoded are stored and replaced. In this way, eachtime stored criteria is used, it is most likely to be as accurate aspossible for that cell.

In a further example, Closed Subscriber Group cells (CSG) cells may betreated differently to non-CSG cells. In the known algorithms, there isno discrimination as to the parameters which can be applied to andretrieved from these cells. In one embodiment, in a similar manner tothat described above, a parameter may be stored separately if it hasbeen decoded from a CSG cell. This parameter may then only be applied tocells which are also CSG cells. In an additional example, the stored CSGcriteria may only be applied to CSG candidate cells operating on thesame frequency as the cell from which the criteria was obtained.Further, the stored CSG criteria may only be applied to CSG candidatecells having the same ID as the cell from which the criteria wasobtained. In this way, the fact that a CSG cell may have significantlydifferent re-selection criteria does not hamper non-CSG cellre-selection; since CSG parameters are not stored and used againstnon-CSG cells and CSG parameters are only applied against CSG cells.

FIG. 7 illustrates this example, in which parameters are applied only toCSG cells only if they are derived from a CSG cell. At step 702, the MSis camped on the serving cell. The MS may first receive a neighbour celllist from the serving cell (step 704). The MS may then decode certainre-selection parameters from the neighbour cell list broadcast by theserving cell (step 706). The MS then identifies a candidate cell andperforms measurements of it, such as signal strength, quality or power(step 708). The candidate cell is a CSG cell. If the cell does not meetthe re-selection requirements, the MS remains camped on the servingcell. If the candidate cell does meet the re-selection requirements(step 710), the MS goes on to check if it has any stored criteriaavailable (step 712). If there are none, the MS continues with there-selection process and tunes to the frequency of the cell to decodesystem information.

The MS then checks if stored criteria are available which were obtainedfrom a CSG cell. (step 714). If not, the MS continues with there-selection process and tunes to the frequency of the cell to decodesystem information.

If the MS has stored criteria obtained from a CSG cell, the candidateCSG cell is checked against these criteria (step 716), for example,using the measurements performed in step 708. If the test is successful,the MS continues with the re-selection process. If it is not, the MSremains camped on the serving cell.

The MS will then, if the conditions described above are met or not asthe case may be, tune to the frequency of the candidate cell and acquiresystem information (step 718). The suitability of the cell forre-selection is then evaluated based on parameters decoded from thesystem information (step 720). If the cell meets the suitabilityrequirements (step 722), the MS may camp on the cell (step 724). If itdoes not, the MS may remain camped on the serving cell (step 702).

Optionally, before acquiring the system information of the candidatecell to decode suitability parameters at step 718, not shown is that theMS may evaluate the candidate cell using default parameters which arenot explicitly signalled. In one example the default parameter is apredetermined amount and is specified in the re-selection specification.If the candidate cell does not meet the requirements based on thisdefault parameter, the MS does not continue with the re-selection andthe MS remains camped on the serving cell. If the MS does meet theserequirements based on the default parameter, the MS continues with there-selection process.

FIG. 8 illustrates a storing process according to the presentdisclosure. In FIG. 8, the step of stopping the process if the cell is aCSG cell is only applied where parameters from CSG cells are not storedor reused. Additionally, the step of deleting previously storedparameters is optional. Although this illustrates storage of CSGcriteria, the illustration is also applicable to non-CSG cells storingfrequency or identity specific parameters, whereby the criteria forstorage of the parameters is altered as required.

With the MS camped on a serving cell (step 802), the MS may decodesystem information of a cell (step 804). The cell, referred to here as‘cell A’ may be a candidate cell which the MS has previously evaluatedor may be any other cell. In a known manner, the MS may evaluate if thecell which the parameters are decoded from, cell A, is of the same or anequivalent PLMN as the serving cell (step 806). If it is not, theparameters may not be stored and the process may stop (step 806). If itis, the process may continue. This ensures that unnecessary parametersare not stored and the network may be able to control the configurationof the stored parameters. Next, in accordance with the present example,the MS will check if the parameters are derived from a CSG cell (step810). If they are, then the process will stop and the parameters willnot be stored (step 812). This is merely one example of the presentdisclosure. Other examples are described herein where the parameter isstored independently of the non-CSG parameters and the CSG parametersare used only to evaluate CSG cells.

In accordance with an earlier described example, the MS may thenidentify the frequency of the cell from which the parameters werederived (step 814). The suitability criteria decoded from the systeminformation are then stored by the MS and associated with the frequencyof the cell for subsequent use (step 816). Any previous parametersassociated with the frequency of this cell, i.e. F_A, may thenoptionally be deleted (step 818). The process may then be finished (step820). The above storing process is equally applicable to the process ofstoring parameters in association with a cell's unique identifier or anycombination of the described applicability of criteria.

In a further example, it is contemplated that cells may broadcast a “donot store” flag to indicate that the MS shall not store parameters forthat cell. This may be useful for, for example test cells, which mayhave very particular or unique settings. Alternatively, there may besome implicit indication or definition of cells for which parametersshould not be stored at all; for example, one or more of the CSG cellsas illustrated in FIG. 8, barred cells or cells where a particularreject cause was received.

Stored values may also be subject to timer expiry, to ensure that storedparameters (in particular, very restrictive parameters) time out anddon't permanently restrict re-selection.

Replacement of stored values by more recently received values may alsobe restricted based on:

-   -   the absolute value of the decoded values    -   the value relative to a previously stored value        (higher/lower/greater than some difference).

This may be useful to prevent storage of obviously very restrictiveparameters or unusual parameters, or to generally ensure that the mostoptimistic values are stored to avoid the device incorrectly abandoningre-selection evaluation based on stored parameters.

The parameters stored by the MS may have been obtained through idle modere-selection or may alternatively have been obtained in connected modeor through some other method. It is described that the parameters areobtained through decoding system information of a cell. This need notalways be the case, for example the parameters could be broadcastseparately from system information. Other methods of obtaining andstoring the parameters to those described above are envisaged.

FIGS. 10 to 14 illustrate certain examples of the present disclosure. Ofcourse it is envisaged that any of these described examples can becombined. FIG. 10 illustrates an MS which first reads the SystemInformation Block (SIB) of a first UTRAN Cell 1. The Qrxlevmin parameteris stored on the MS and associated with the Frequency, FREQ1, of UTRANCell 1 where the parameters came from. The MS remains on the GSM servingcell, perhaps because Cell 1 is not appropriate for re-selection;however the reason is irrelevant. The MS then evaluates UTRAN Cell 2 forre-selection. If the frequency of Cell 2, FREQ2, is equal to FREQ1, thenthe MS uses the stored Qrxlevmin value to evaluate Cell 2. Not shown isthat, if the evaluation is successful, the MS will re-select to Cell 2or alternatively, the MS will continue or complete the re-selectionprocess towards Cell 2 because it may not be conclusive after this testthat re-selection will be successful. Also not shown is that if thefrequencies are not equal, the evaluation is performed without thestored parameter.

FIG. 11 illustrates an MS which first reads the SIB of a first UTRANCell 1. The Qrxlevmin parameter is stored on the MS and associated withthe identity, ID1, of UTRAN Cell 1 where the parameters came from. Theidentity ID1 may, for example, be the scrambling code. The MS remains onthe GSM serving Cell. The MS then evaluates UTRAN Cell 2 forre-selection. If the Cell_ID of Cell 2, ID2, is equal to ID1, then theMS uses the stored Qrxlevmin value to evaluate Cell 2. Not shown isthat, if the evaluation is successful, the MS will re-select to Cell 2.Also not shown is that if the Cell_IDs are not equal, the evaluation isperformed without the stored parameter.

FIG. 12 illustrates an example of the present disclosure relating to CSGcells. The MS first decodes the System Information Block (SIB) of afirst UTRAN cell. The MS stores the Qrxlevmin as the cell is a UTRANcell and not a CSG cell. The MS then decodes the SIB of a CSG cell(which may also be a UTRAN cell). In this example, the Qrxlevmin is notstored since the cell is a CSG cell. The MS then evaluates the UTRANcell for re-selection. The MS uses the stored Qrxlevmin value obtainedfrom the first UTRAN Cell in the evaluation, since this was stored andthe Qrxlevmin from the CSG cell was not.

FIG. 13 illustrates another example of the present disclosure relatingto CSG cells. The MS reads the SIB of a first CSG Cell 1 and decodes theSIB. The MS then stores the Qrxlevmin and associates it in its datastore with an indication that the parameter was obtained from a CSGcell. The MS remains camped on the serving cell, in this case a GSMcell. The MS then evaluates a second CSG Cell 2 for re-selection usingthe stored Qrxlevmin value since Cell 2 is a CSG cell.

FIG. 14 illustrates another example of the present disclosure. The MS iscamped on a GSM cell. The MS reads and decodes the SIB of a first CSGCell 1. The MS then stores the Qrxlevmin and associates it in the datastore with an indication that the cell is a CSG Cell and the Cell_ID ofthe cell, ID1, from which the Qrxlevmin is derived. The MS remainscamped on the GSM Cell. The MS then evaluates a second CSG Cell 2 forre-selection using the stored Qrxlevmin only if the cell is a CSG celland the Cell_ID of the second cell, ID2, equals ID1. Preferably, thefrequency of the cell and the Cell_ID may be considered jointly asdescribed above, for example, the CSG cell may be evaluated using storedparameters only if the frequency and the Cell_ID of the cell from whichthe parameters were obtained are the same as those for the candidatecell.

A specific exemplary implementation of an example of the presentdisclosure will now be described. In a multi RAT system, whenever the UEattempts to camp on a UTRAN FDD cell (and/or is camped on the cell,and/or has any other reason to read the SIB of a UTRAN FDD cell) itdecodes the RSCP criterion parameters from SIBs and stores it for futureuse. The UE may store the frequency of the cell in addition to otherparameters. When a UE moves to 2G, the UE can start applying the storedsuitability criteria parameters for 2G to 3G cell re-selections towardsall UTRAN FDD cells configured on the frequency for which lastinformation was stored.

Currently only the RSCP criterion is stored and used in the system butwith this change the UE needs to store the frequency associated withRSCP criterion. The UE may have to maintain a list of frequency andassociated RSCP criterion parameters. If the UE subsequently reads theSIB of another UTRAN FDD cell operating on a frequency for which it hasstored suitability parameters, then it may replace the stored valueswith those from the SIBs it has just read. The list will get clearedafter PLMN selection (see 3GPP TS 23.122).

The present disclosure reduces the chances of a device being stuck in 2Gin certain configurations, provides improved flexibility to operators inconfiguring suitability criteria (since these will only be used forother cells of the same frequency) and allows 2G to 3G cell re-selectionto non “restricted” frequencies of the PLMN in the case where certainfrequencies are “restricted” by means of high suitability thresholds.

Considering the scenario of cells A, B and C described above, where cellB is the serving cell, cell A is a cell from which parameters havepreviously been decoded and cell C is the current candidate cell, theparameters associated with Cell A may be:

PLMN ID (referred to as PLMN_A],

Frequency, [F_A]

Physical layer address (PCI/PSC) [P_A] or

Whether it is a CSG cell [is CSG_A].

These parameters may all be determined by decoding the systeminformation (SIB) of cell A. The system information is generic and maybe derived from other blocks than the SIB referred to throughout thepresent disclosure. The PLMN rules in these examples are merelyexemplary and are not necessary to the present disclosure. They are anadditional, independent constraint.

The parameters associated with Cell B, which is the serving cell in thisexemplary scenario, may be:

PLMN ID, [PLMN_B]; or

[Frequency, Physical layer address (PCI/PSC) which is relevant only ifCell B is of the same RAT as Cells A,C].

The parameters associated with Cell C may be:

Frequency, [F_C];

Physical layer address (PCI/PSC) [P_C]; Whether it is a CSG cell [isCSG_C]—This may only be determinable either based on F_C, or, based onP_C and knowledge of the range of physical layer addresses reserved forCSG cells; or

[PLMN_C which may not be known at the time when the initial evaluationof radio signal quality/strength is carried out].

Typically, the conventional specifications specify that the parametersfrom Cell A can be used to evaluate Cell C if PLMN_A=PLMN_B or PLMN_Aand PLMN_B are equivalent.

One of the examples of the disclosure is to modify this rule to be thatparameters from Cell A can be used to evaluate Cell C if

i) PLMN_A=PLMN_B or PLMN_A and PLMN_B are equivalent and

ii) F_A=F_C.

Considering another example, illustrated in FIG. 8, taking into accountCSG cells, this can be expressed as: Parameters from Cell A can be usedto evaluate Cell C if

i) PLMN_A=PLMN_B or PLMN_A and PLMN_B are equivalent, and

ii) F_A=F_C, and

iii) neither Cell A nor cell C are CSG cells (i.e. is CSG_A=False and isCSG_C=False)

A further example relating to CSG cells (which, in effect, states thatcells A and C must be both CSG cells), can be expressed as: Parametersfrom Cell A can be used to evaluate Cell C if

i) PLMN_A=PLMN_B or PLMN_A and PLMN_B are equivalent, and

ii) F_A=F_C, and

iii) both Cell A and cell C are CSG cells (i.e. is CSG_A=True and isCSG_C=True)

A further example relating to CSG cells (which, in effect, states thatcells A and C must be, with high probability, the same cell), can beexpressed as the above conditions in addition to:

iv) P_A=P_C

Further modifications to the above rules can be considered, to addressthe case where different (but equivalent) PLMNs have differentre-selection criteria, by modifying rule i) in each or any combinationof the cases above to:

i) PLMN_A=PLMN_B

In a further example of the present disclosure, previously storedsuitability requirements (which may have been obtained as a result ofranking-based re-selection) shall not be used when evaluating cellsaccording to priority-based re-selection rules. In a priority-basedre-selection algorithm, threshold parameters may be broadcast in theserving cell, as described above. In the present example, therestriction on the use of stored suitability parameters may be dependenton whether the corresponding (signal quality/signal strength) parametersare available in the current serving cell, for example, broadcast by thecell. This is not always the case.

FIG. 9 illustrates this particular example. The process may optionallybegin with an MS attempting re-selection to a 3G cell. The MS receivesthe System Information Blocks (SIBs) from the 3G cell (step 904) andthen decodes and stores the Received Signal Code Power (RSCP) criteriaparameters (step 906). The MS may then evaluate a candidate 3G cellusing the priority-based re-selection rules in the known manner (step908).

Conventionally, the MS will then evaluate the candidate cell againststored RSCP criteria (step 912) and, if the cell does not meet thecriteria based on the stored RSCP parameters (step 914), the processwill stop and the MS will not re-select to the cell (step 916). If thecandidate cell does meet the criteria (step 914), then the cell will beevaluated to see if it meets the priority-based re-selection criteria,as stated in section 6.6.6. of the 45.008 specification.

According to the present disclosure, however, the steps covered by thearea marked 910, are not to be carried out. According to the presentdisclosure, in a priority-based re-selection algorithm, the candidatecell is not to be evaluated using stored threshold criteria. Thesecriteria may have been obtained as part of a ranking-based algorithm andby decoding system information from another cell, or the same cell.

In the present example, when the MS has evaluated a candidate cell usingthe priority-based re-selection rules (step 908), it then determines ifthe candidate cell meets the priority-based re-selection criteriaregardless, or irrespective, of any stored parameters (step 918). If thecell does not meet the criteria, the evaluation ends and the MS does notre-select to the cell (step 916). If the candidate cell does meet there-selection criteria in accordance with the priority-based re-selectionrules, the MS performs re-selection to the cell (step 920).

In this way, the priority-based re-selection algorithm is not hamperedby incorrect parameters, which may have been stored during ranking-basedre-selection. If the parameters are broadcast by the serving cell, theywould remain the primary criteria to be used in priority-basedre-selection. If parameters are not broadcast, then the MS shoulddetermine the appropriateness of the cell for re-selection without usingstored parameters which may be untrustworthy.

FIG. 15 illustrates an MS which first reads the System Information Block(SIB) of a UTRAN Cell while camped on a first GSM Cell 1. In GSM Cell 1only ranking algorithms are used for re-selection to UTRAN cells. TheQrxlevmin parameter is stored on the MS. The MS may perform re-selectionfrom the GSM cell 1 to a second GSM Cell 2. The GSM Cell 2 supportspriority-based re-selection. From the GSM Cell 2, the MS may evaluatethe UTRAN cell using priority-based re-selection. When performing thepriority-based evaluation, the MS will not use the stored criteria thatwere obtained from the UTRAN cell during the ranking algorithm. Notshown is that, if the evaluation is successful, the MS will re-select tothe UTRAN Cell.

An exemplary algorithm which may be used to implement the principles ofthe above disclosure will now be described. Although the language of thealgorithm which this example builds on may be altered or clarified, theprinciples illustrated by the text which has been inserted and alteredwhen compared to the original algorithm are equally applicable to anyamended algorithm.

This is an algorithm for cell re-selection from GSM to UMTS based oncell ranking. The algorithm in this subclause shall be used forre-selection from GSM to UMTS if the conditions for the use of the cellre-selection algorithm based on priority information are not satisfied.

If the 3G Cell Re-selection list includes UTRAN frequencies, the MSshall, at least every 5 s update the value RLA_C for the serving celland each of the at least 6 strongest non serving GSM cells.

The MS shall then reselect a suitable (see 3GPP TS 25.304) UTRAN cell if

for a TDD cell the measured RSCP value is equal to or greater thanTDD_Qoffset for a period of 5 s and

for an FDD cell the following criteria are all met for a period of 5 s:

-   -   1. its measured RSCP value exceeds the value of RLA_C for the        serving cell and all of the suitable (see 3GPP TS 43.022)        non-serving GSM cells by the value FDD_Qoffset,    -   2. its measured Ec/No value is equal or greater than the value        FDD_Qmin−FDD_Qmin_Offset, and

3. its measured RSCP value is equal to or greater thanFDD_RSCP_threshold.

In case of a cell re-selection occurring within the previous 15 seconds,FDD_Qoffset or TDD_Qoffset is increased by 5 dB.

Ec/No and RSCP are the measured quantities, see subclause 8.1.5.

-   -   FDD_RSCP_threshold equals FDD_RSCPmin−min((P_MAX−21 dBm), 3 dB)        if FDD_RSCPmin is broadcast on the serving cell, else        Qrxlevmin+Pcompensation+10 dB, if these parameters are        available, otherwise the default value of FDD_RSCPmin.    -   Qrxlevmin is the minimum required RX level in the UTRAN FDD cell        (dBm), see 3GPP TS 25.304.    -   Pcompensation is max(UE_TXPWR_MAX_RACH−P_MAX, 0) (dB), see 3GPP        TS 25.304.    -   UE_TXPWR_MAX_RACH is the maximum TX power level an MS may use        when accessing the UTRAN FDD cell on RACH (dBm), see 3GPP TS        25.304.    -   P_MAX is the maximum RF output power of the MS (dBm) in UTRAN        FDD mode, see 3GPP TS 25.304.    -   FDD_Qmin, FDD_Qoffset and optionally FDD_RSCPmin and        FDD_Qmin_Offset are broadcast on BCCH of the serving cell.    -   TDD_Qoffset is broadcast on BCCH of the serving cell.

Note 1: The parameters required to determine if the UTRAN cell issuitable are broadcast on BCCH of the UTRAN cell. An MS may startre-selection towards the UTRAN cell before decoding the BCCH of theUTRAN cell, leading to a short interruption of service if the UTRAN cellis not suitable.

Note 2: If FDD_RSCPmin is broadcast, optimum GSM to UTRAN re-selectionperformance is achieved if UTRAN cells at UTRAN coverage border areasare planned for +24 dBm UE power.

Note 3: The parameter TDD_Qoffset is an absolute threshold forre-selection towards a target UTRAN TDD cell.

The MS shall store the UTRAN cell RSCP suitability criterion parametersabove, whenever decoded from a UTRAN FDD cell of an equivalent PLMNwhile attempting to camp on the UTRAN FDD cell unless the cell is a CSGcell/indicates ‘do not store’/is unsuitable because {it is part of the“list of forbidden LAs for roaming”} or it is barred/or would result ina FDD_RSCP_threshold which is [greater than that currently stored forcells on the same frequency/greater than [XX] dB. The most recentlystored parameters from a UTRAN FDD cell of an equivalent PLMN are validre-selection criteria towards all UTRAN FDD cells except CSG cells andcells evaluated according to the priority-based re-selection algorithm(see sub-clauses 6.6.7 and 6.6.6 respectively). Stored values which werereceived more than [5] minutes ago shall be cleared. This list ofparameters shall be cleared after PLMN selection (see 3GPP TS 23.122).

It should be noted that the “/” here is used to distinguish differentaspects of the disclosure, though they may be combinable.

Cell re-selection to UTRAN shall not occur within 5 seconds after the MShas reselected a GSM cell from an UTRAN cell if a suitable GSM cell canbe found.

In case of a re-selection attempt towards a barred UTRAN cell, the MSshall abandon further re-selection attempts towards this UTRAN cell asdefined by the T_(barred) value on the barred UTRAN cell (see 3GPP TS25.331).

In case the highest ranked UTRAN cell is not suitable (see 3GPP TS25.304) due to being part of the “list of forbidden LAs for roaming” orbelonging to a PLMN which is not indicated as being equivalent to theregistered PLMN, the MS may abandon further re-selection attemptstowards this UTRAN cell and all other cells on the same frequency, for aperiod of up to 20 min. If the MS has to perform cell selection, thislimitation shall be removed. If the MS is redirected under GERAN controlto a frequency for which the timer is running, any limitation on thatfrequency shall be removed.

If more than one UTRAN cell fulfils the above criteria, the MS shallselect the cell with the greatest RSCP value.

A further exemplary algorithm which may be used to implement theprinciples of the above disclosure will now be described. Although thelanguage of the algorithm which this example builds on may be altered orclarified, the principles illustrated by the text which has beeninserted and altered when compared to the original algorithm are equallyapplicable to any amended algorithm.

This is an algorithm for inter-RAT cell re-selection based on priorityinformation. The algorithm in this subclause shall be used for inter-RATcell re-selection if priorities are available to the MS and thresholdsare provided by the network, and if the mobile station supports prioritybased inter-RAT cell re-selection and priority information for theserving cell is provided by the network. A mobile station supportingE-UTRAN shall support priority based inter-RAT cell re-selection towardsall the supported RATs. A mobile station not supporting E-UTRAN andsupporting UTRAN and supporting priority based re-selection from UTRANto GERAN shall support priority based inter-RAT cell re-selectiontowards UTRAN.

The network shall provide priority information if E-UTRAN frequenciesare included in the neighbour cell list; the network may providepriority information if only UTRAN frequencies are included in theneighbour cell list. If priority information is available to the mobilestation and the mobile station supports priority based inter-RAT cellre-selection, the algorithm in this subclause shall be used forinter-RAT_re-selection towards all RATs. The rules regarding which setof priorities is valid at any given time are defined in 3GPP TS 44.018.

NOTE 1: “Priority information” includes priorities and thresholds whichare related to each UTRAN or E-UTRAN frequency (e.g. UTRAN_PRIORITY,E-UTRAN_PRIORITY, THRESH_UTRAN_high, THRESH_E-UTRAN_high) andinformation related to the serving cell (e.g. GERAN_PRIORITY,THRESH_GSM_low).

NOTE 2: Throughout the specification, the phrase “neighbour cell list”will include also the E-UTRAN Neighbour Cell list where appropriate.

NOTE 3: Priorities need to be provided also for frequencies of networksthat do not support priority-based cell re-selection.

If the 3G Cell Re-selection list or the E-UTRAN Neighbour Cell listincludes frequencies of other radio access technologies, the MS shall,at least every 5 s update the value RLA_C for the serving cell and eachof the at least 6 strongest non serving GSM cells.

The MS shall then reselect a suitable (see 3GPP TS 25.304 for UTRAN and3GPP TS 36.304 for E-UTRAN) cell of another radio access technology ifthe criteria below are satisfied. S_non-serving_XXX is the measurementquantity of a non-serving inter-RAT cell and XXX indicates the otherradio access technology/mode and is defined as follows:

for a UTRAN cell, is the measured RSCP value for the cell minusUTRAN_QRXLEVMIN for the cell's frequency;

for a E-UTRAN cell, is the measured RSRP value for the cell minusE-UTRAN_QRXLEVMIN for the cell's frequency if THRESH_E-UTRAN_high_Q isnot provided; otherwise, if THRESH_E-UTRAN_high_Q is provided, is themeasured RSRQ value for the cell minus E-UTRAN_QQUALMIN for the cell'sfrequency.

Stored suitability requirements (e.g. such RSCP suitability requirementsstored as specified in sub-clause 6.6.5) shall not be used for UTRANcells when evaluating cells according to the criteria in thissub-clause.

For a GSM cell, S_GSM is defined as the C1 value for the cell (seesubclause 6.4);

Cell re-selection to a cell of another inter-RAT frequency shall beperformed if any of the conditions below (to be evaluated in the ordershown) is satisfied:

The S_non-serving_XXX of one or more cells of a higher priorityinter-RAT frequency is greater than THRESH_XXX_high (or, in case of anE-UTRAN target, THRESH_E-UTRAN high_Q, if provided) during a timeinterval T_re-selection; in that case, the mobile station shall considerthe cells for re-selection in decreasing order of priority and, forcells of the same inter-RAT frequency or of inter-RAT frequencies ofequal priority, in decreasing order of S_non-serving_XXX and reselectthe first cell that satisfies the conditions above;

The value of S_GSM is lower than THRESH_GSM_low for the serving cell andall measured GSM cells during a time interval T_re-selection; in thiscase, the mobile station shall consider for re-selection the inter-RATcells in the following order, and reselect the first one that satisfiesthe following criteria:

cells of a lower priority inter-RAT frequency whose S_non-serving_XXX isgreater than THRESH_XXX_low (or, in case of an E-UTRAN target,THRESH_E-UTRAN_low_Q, if provided) during a time intervalT_re-selection; these cells shall be considered in decreasing order ofpriority and, for cells of the same RAT, in decreasing order ofS_non-serving_XXX;

if no cells satisfy the criterion above, inter-RAT cells for which,during a time interval T_re-selection, S_non-serving_XXX is higher thanS_GSM for the serving cell by at least a specific hysteresis H_PRIO;these cells shall be considered in decreasing order ofS_non-serving_XXX.

A UTRAN FDD cell shall only be reselected if, in addition to thecriteria above, its measured Ec/No value is equal to or greater thanFDD_Qmin−FDD_Qmin_Offset.

If E-UTRAN_Qmin is provided for a E-UTRAN frequency, a E-UTRAN cell onthat frequency shall only be reselected if, in addition to the criteriaabove, its measured RSRQ value is equal to or greater than E-UTRAN_Qmin.A mobile station shall store {all/RSRQ-related}suitability requirementsfrom an E-UTRAN cell on the same PLMN or on an equivalent PLMN as thatof the serving cell[, to which it has attempted re-selection] [unless itreceived an indication from that cell e.g. in system information thatsuitability requirements for that cell shall not be stored] [or the cellwas a CSG cell] [or was not suitable]. When evaluating an E-UTRAN cell,the most recently-stored RSRQ-related suitability requirements receivedfrom an E-UTRAN cell [other than those obtained from a CSG cell] on thesame frequency/frequency of the same priority shall be used ifE-UTRAN_Qmin is not provided by the serving cell.

If THRESH_E-UTRAN_high_Q is provided for a E-UTRAN frequency, and ifE-UTRAN_RSRPmin is provided, a E-UTRAN cell on that frequency shall onlybe reselected if, in addition to the criteria above, its measured RSRPvalue is equal to or greater than E-UTRAN_RSRPmin. If E-UTRAN_RSRPmin isnot provided, the default value shall be used.

E-UTRAN cells which are included in the list of not allowed cells shallnot be considered as candidates for cell re-selection. If the strongestcells on a E-UTRAN frequency are included in the list of not allowedcells, the mobile station may reselect the strongest valid cell (seesubclause 8.4.7) on that frequency.

Cell re-selection to a cell of another radio access technology (e.g.UTRAN or E-UTRAN) shall not occur within 5 seconds after the MS hasreselected a GSM cell from an inter-RAT cell if a suitable GSM cell canbe found.

If the mobile station applies either common priorities or individualpriorities received through dedicated signalling and priorities areavailable only for some inter-RAT frequencies, cells belonging tofrequencies for which no priority is available or no threshold isprovided by the serving cell shall not be considered for measurement andfor cell re-selection.

If a mobile station in camped normally state (see 3GPP TS 43.022)applies individual priorities received through dedicated signalling andno priority is available for the serving cell, the mobile station shallconsider any GSM cell (including the serving cell) to have lowestpriority (i.e. lower than the eight network configured values).

A mobile station in camped on any cell state (see 3GPP TS 43.022) shallignore individual priorities received through dedicated signalling andshall apply priorities received from the system information of theserving cell while attempting to find a suitable cell. If the mobilestation supports CS voice services, the MS shall avoid reselectingacceptable (but not suitable) E-UTRA cells regardless of the prioritiesprovided in system information.

NOTE 4: If the MS is camping on an acceptable cell, individualpriorities are not discarded until an event leading to their deletionoccurs.

In case of a re-selection attempt towards a barred UTRAN cell, the MSshall abandon further re-selection attempts towards this UTRAN cell asdefined by the T_(barred) value on the barred UTRAN cell (see 3GPP TS25.331).

In case of a re-selection attempt towards a barred E-UTRAN cell, the MSshall abandon further re-selection attempts towards this E-UTRAN cellfor a period of up to 20 min.

In case the MS attempts re-selection to a UTRAN cell which is notsuitable (see 3GPP TS 25.304) due to being part of the “list offorbidden LAs for roaming” or belonging to a PLMN which is not indicatedas being equivalent to the registered PLMN, the MS may abandon furtherre-selection attempts towards this UTRAN cell and all other cells on thesame frequency, for a period of up to 20 min. If the MS has to performcell selection, this limitation shall be removed. If the MS isredirected under GERAN control to a frequency for which the timer isrunning, any limitation on that frequency shall be removed.

In case the MS attempts re-selection to a E-UTRAN cell which is notsuitable (see 3GPP TS 36.304) due to being part of the “list offorbidden tracking areas for roaming” (see 3GPP TS 24.301), and if theMS has received the PCID to TA Mapping information element (see 3GPP TS44.018 and 3GPP TS 44.060) for the frequency of the cell, it shallabandon further re-selection attempts towards this E-UTRAN cell and anyE-UTRAN cell which is known to belong to the same Tracking Area untilthe PCID to TA Mapping information changes in the serving cell or untilcell re-selection occurs. If the mobile station has not received thePCID to TA Mapping information element for the frequency of the cell,the MS may abandon further re-selection attempts towards this E-UTRANcell and all other cells on the same frequency, for a period of up to 20min. If the MS has to perform cell selection, this limitation shall beremoved. If the MS is redirected under GERAN control to a frequency forwhich the timer is running, any limitation on that frequency shall beremoved.

In case the MS attempts re-selection to a E-UTRAN cell which is notsuitable (see 3GPP TS 36.304) due to belonging to a PLMN which is notindicated as being equivalent to the registered PLMN, the MS may abandonfurther re-selection attempts towards this E-UTRAN cell and all othercells on the same frequency, for a period of up to 20 min. If the MS hasto perform cell selection, this limitation shall be removed. If the MSis redirected under GERAN control to a frequency for which the timer isrunning, any limitation on that frequency shall be removed.

A further exemplary algorithm which may be used to implement theprinciples of the above disclosure will now be described. Although thelanguage of the algorithm which this example builds on may be altered orclarified, the principles illustrated by the text which has beeninserted and altered when compared to the original algorithm are equallyapplicable to any amended algorithm.

This is an algorithm for cell selection and re-selection to CSG cellsand hybrid cells. Firstly, for cell re-selection to CSG cells, if amobile station is a member of at least one Closed Subscriber Group, i.e.at least one CSG ID is included in the MS's CSG Whitelist, then, inaddition to normal cell re-selection, the MS shall use an autonomoussearch function to detect UTRAN and/or E-UTRAN CSG cells. The autonomoussearch function shall at least detect previously visited allowed CSGcells, according to performance requirements.

NOTE 1: The autonomous search function is implementation dependent andcontrols when and/or where to search for allowed CSG cells.

NOTE 1a: (void).

NOTE 2: (void).

NOTE 3: (void).

If the strongest cell (see 3GPP TS 25.304 and 3GPP TS 36.304 for thedefinition of the strongest cell) which the MS has detected on a UTRANor E-UTRAN frequency during a time interval T_re-selection is a suitableCSG cell (see 3GPP TS 25.304 and 3GPP TS 36.304 for suitability criteriafor UTRAN and E-UTRAN CSG cells respectively), it should reselect tothis cell irrespective of the cell re-selection rules applicable for thecell on which the MS is currently camped.

The MS shall disable the autonomous search function for CSG cells if theMS has no CSG Whitelist or the MS's CSG Whitelist is empty.

When the MS has no or an empty CSG Whitelist, and the MS has stored “CSGPSC Split Information” or “CSG PCI Split Information”, the MS shallignore for measurement and cell re-selection cells known to be CSGcells, i.e.:

cells on a UTRAN frequency with PSC in the stored range “CSG PSC SplitInformation” for that frequency (see 3GPP TS 25.331);

cells on an E-UTRAN frequency with PCI in the stored range “CSG PCISplit Information” for that frequency (see 3GPP TS 36.331).

In addition, when the MS has no or an empty CSG Whitelist, the MS mayignore for measurement and cell re-selection cells known to be CSG cellsaccording to implementation specific means on a frequency for which no“CSG PCI Split Information” or “CSG PSC Split Information” is stored.

The network may provide information about dedicated UTRAN CSGfrequencies and/or dedicated E-UTRAN CSG frequencies. In this case, theMS may use the autonomous search function only on these dedicatedfrequencies and on the other frequencies listed in the systeminformation. When the MS has no or an empty CSG Whitelist, the MS shallignore those frequencies for measurement and cell re-selection.

A mobile station shall store the RSRP/RSCP/RSRQ [i.e. signal qualityand/or signal strength] related suitability requirements received from aCSG cell; these shall be maintained independently of criteria stored fornon-CSG cells. When evaluating a CSG cell, the mobile station shall usethe most recently-stored values from a [CSG] cell {on the samefrequency/with the CSG ID. or When evaluating a CSG cell, the mobilestation shall use the stored values from the same cell (or a cell withthe same frequency and PCI/PSC) {provided these were received less than[2] minutes ago.

Secondly, for cell re-selection to hybrid cells, if a mobile station isa member of at least one Closed Subscriber Group then, in addition tonormal cell re-selection, the MS shall use an autonomous search functionto detect hybrid cells. The autonomous search function shall at leastdetect previously visited hybrid cells whose CSG IDs are included in theCSG whitelist of the MS, according to the performance requirements.

NOTE: The autonomous search for hybrid cells does not imply that the MSneeds to constantly check the CSG IDs of all cells it sees, and theimpact on battery consumption should be minimised.

If a neighbour cell has been detected as a hybrid cell and the CSG ID ofthe hybrid cell is included in the CSG Whitelist of the MS, re-selectionto that cell shall follow the rules for CSG cells in subclause 6.6.7.1.Otherwise normal cell re-selection rules shall apply.

Thirdly, for manual CSG ID selection, if NAS requests AS to search foravailable CSG IDs, the MS shall perform the search and report theresults to NAS as described in 3GPP TS 25.304 for UTRAN and as describedin 3GPP TS 36.304 for E-UTRAN. If a CSG ID is manually selected by NAS,the MS shall behave as specified in 3GPP TS 25.304 or in 3GPP TS 36.304,depending on the RAT type of the selected CSG cell.

A further example of the present disclosure will now be described.

In some cases, as part of the typically known re-selection algorithm,the device is required to evaluate one or more aspects of the targetcell (such as signal quality or signal strength, etc.) based onparameters such as thresholds broadcast by the serving cell (in thisexemplary scenario, cell B).

However, it currently is required to re-evaluate these aspects once ithas read the system information from the candidate cell (cell C), aspart of the suitability check (since the suitability criteria includetests based on parameters broadcast by the candidate cell). This resultsin the device evaluating the same aspects twice. In a well-configurednetwork, the parameters should be such that a cell which meets there-selection criteria (based on parameters broadcast in the servingcell) should not fail the corresponding tests based on parametersbroadcast in the candidate cell. In this scenario, the second test isredundant.

However, and furthermore, if the device performs both evaluations andfails the second test (i.e. based on parameters broadcast in thecandidate cell C), it will return to the serving cell. It may thenrepeat this process endlessly until cell C no longer meets the criteriabased on the parameters broadcast by cell B. This is likely an incorrectconfiguration of the network. In this scenario, the second test mayresult in the mobile station repeatedly attempting re-selection to thesame cell.

Storage and re-use of parameters from cells A or C may address thislatter problem, however, no provision is currently made in thepriority-based re-selection scheme for storage of criteria from acandidate cell (see 6.6.6 of 45.008).

Furthermore, as noted elsewhere, storage of the suitability criteriabroadcast by cell C in this scenario may cause incorrect abandonment ofre-selection attempts to other cells (i.e. other than cell C), since alikely problem here is that cell C's suitability criteria (as determinedbased on parameters transmitted by cell C) are incorrectly set such thatthe criteria are too high.

In a further exemplary implementation of the disclosure, it would bepreferable for the device not to carry out some or any tests (e.g. aspart of the test for suitability) based on criteria broadcast by cell C,if the criteria for re-selection based on parameters broadcast in theserving cell have already been tested and met. If re-selection criteriaare met and the subset of suitability criteria are met, the device mayremain camped in the candidate cell, irrespective of the value(s) of theparameter(s) associated with the skipped suitability check(s) broadcastin the candidate cell. This process is illustrated in FIG. 16.

As a further exemplary implementation: it should omit only thosesuitability tests which evaluate specific aspects (signal strength,signal quality) which were tested as part of the re-selection procedure.In some cases, only one of signal strength/quality might be tested aspart of the re-selection algorithm.

As yet a further exemplary implementation it should omit only thosetests which evaluate specific aspects (signal strength, signal quality)which were tested as part of the re-selection procedure and which werebased on parameters which were broadcast or transmitted by the servingcell (as opposed to using default, standardised values).

As a further exemplary implementation, the above exception may applyonly to “threshold-based” tests (i.e. where a measured quantity of thecandidate cell must meet or exceed some determined absolute value), butnot to “relative value” tests—e.g. where a measured value must exceedsome other measured value (of the candidate cell, serving cell and/orone or more other cells) by some minimum difference.

In an exemplary scenario of the latter exemplary implementation, for CSGcells, a candidate CSG cell may meet the re-selection criteria if it isthe strongest on its frequency. This is considered a ‘relative’ test ofsignal strength, rather than an absolute test.

In typical conventional networks, that a device may currently berequired to check suitability criteria twice: once using stored values(obtained from the same, or a different cell), and once using valuesreceived from the candidate cell once it has decoded the relevant systeminformation.

Currently, there is a relatively high risk that the suitabilityparameters stored by the device and used for the initial evaluation ofsuitability (i.e. before system information of candidate cell has beenreceived) may be different from those broadcast by the candidate cellitself. It is therefore reasonably possible that the suitabilitycriteria may be met in respect of the first test, but not for thesecond.

In a further exemplary implementation of the disclosure which isillustrated in FIG. 16, if a restriction on the usage of storedparameters from cell A when evaluating cell C is in place (such as, theymust be on the same frequency, or both must be non-CSG cells), then therisk that the parameters are different is significantly lowered.Therefore, according to this exemplary implementation of the disclosure,to further reduce the need for evaluation of parameters and/or to reducethe risk that a device determines (based on stored parameters) toperform re-selection, acquires system information of the candidate cell,and then determines that the re-selection is not possible. The devicemay omit the second suitability check. This is similar to the omissionin the preceding exemplary implementation of the disclosure.

This may be conditional on the frequency of cell A and cell C being thesame; optionally, further criteria may apply—such as the physical layeraddress of cell A and cell C must be the same; in general, any suitablecriteria can be used, such as those listed above.

A further condition may be that cell A and cell C were both re-selectioncandidates while the device was initially camped in cell B—for example,in the following case:

i) device is camped in cell B

ii) device attempts re-selection to cell A; reads suitability criteriafor cell A and determines these are not met; remains in cell B

iii) device attempts re-selection to cell C—cell C and cell A operate onthe same frequency; cell C meets the suitability criteria as obtainedfrom cell A; device does not re-evaluate suitability criteria based onparameters obtained from cell C. (In other words, the device camps oncell C independent of the suitability parameters signalled by cell C).

It is worth noting that if operators coordinate the configuration ofsuitability parameters for cells across a serving PLMN and equivalentPLMNs to such an extent that these parameters are similar across allcells, then this solution may be applicable even without any constraintson cell A and cell C.

In FIG. 16, the illustrated process starts with the MS camped on aserving cell, cell B (step 1602). The MS may then optionally receive aneighbour cell list from the serving cell (step 1604). The MS thendecodes re-selection parameters from the list (step 1606). The MS willthen identify a candidate cell and perform measurements on it (step1608). If the cell does not meet re-selection criteria, the MS remainscamped on the serving cell (step 1610). If the criteria are met, the MSchecks if it has stored suitability parameters available (step 1612). Ifthe MS has stored suitability parameters available, the MS checks thecell against these criteria (step 1614). If the criteria are not met,the MS remains camped on the serving cell. If the criteria are met orthe MS does not have parameters stored and available for testing, the MSmoves on to acquiring system information of the candidate cell (step1616).

After acquiring system information, the MS considers radio relatedaspects such as signal strength or quality (step 1618). If these wereevaluated when determining if the cell met re-selection criteria (step1620) and the evaluation was not based on default parameters which werenot explicitly signalled (step 1622) then the MS moves on to checkanother radio related aspect (step 1626). If there are no more aspects,then the cell is determined to meet the criteria (step 1632) andnon-radio related criteria are evaluated (step 1634). In this way, ifsignalled criteria was used and checked against radio-related aspectsthen the MS does not re-determine the suitability.

If the radio related aspects were not evaluated when determining if thecell met re-selection criteria (step 1620) and if the evaluation usedstored suitability parameters (step 1624), then the MS moves on to checkanother radio related aspect (step 1626). If there are no more aspects,then the cell is determined to meet the criteria (step 1632) andnon-radio related criteria are evaluated (step 1634). In this way, ifsignalled criteria was used and checked against radio-related aspectsthen the MS does not re-determine the suitability.

If the radio related aspects were evaluated when determining if the cellmet re-selection criteria (step 1620) and the evaluation was based ondefault parameters which were not explicitly signalled (step 1622), thenthe MS checks if the evaluation used stored suitability parameters (step1624). If it did, the MS moves on to check another radio related aspect(step 1626). If there are no more aspects, then the cell is determinedto meet the criteria (step 1632) and non-radio related criteria areevaluated (step 1634). In this way, if signalled criteria was used andchecked against radio-related aspects then the MS does not re-determinethe suitability.

If the MS did not use stored suitability parameters (step 1624), the MSevaluates the cell using parameters from the candidate cell's systeminformation (step 1628), by establishing a communication channel anddecoding the parameters. If the cell does not meet the criteria, it isdetermined to be unacceptable and the MS remains camped on the servingcell (step 1636). If it does meet the criteria, the MS moves on to checkanother radio related aspect (step 1626). If there are no more aspects,then the cell is determined to meet the criteria (step 1632) andnon-radio related criteria are evaluated (step 1634). In this way, ifsignalled criteria was used and checked against radio-related aspectsthen the MS does not re-determine the suitability.

An exemplary algorithm for implementing examples of the presentdisclosure will now be described. This is an algorithm for inter-RATcell re-selection based on priority information.

The algorithm in this subclause shall be used for inter-RAT cellre-selection if priorities are available to the MS and thresholds areprovided by the network, and if the mobile station supports prioritybased inter-RAT cell re-selection and priority information for theserving cell is provided by the network A mobile station supportingE-UTRAN shall support priority based inter-RAT cell re-selection towardsall the supported RATs. A mobile station not supporting E-UTRAN andsupporting UTRAN and supporting priority based re-selection from UTRANto GERAN shall support priority based inter-RAT cell re-selectiontowards UTRAN.

The network shall provide priority information if E-UTRAN frequenciesare included in the neighbour cell list; the network may providepriority information if only UTRAN frequencies are included in theneighbour cell list. If priority information is available to the mobilestation and the mobile station supports priority based inter-RAT cellre-selection, the algorithm in this subclause shall be used forinter-RAT_re-selection towards all RATs. The rules regarding which setof priorities is valid at any given time are defined in 3GPP TS 44.018.

NOTE 1: “Priority information” includes priorities and thresholds whichare related to each UTRAN or E-UTRAN frequency (e.g. UTRAN_PRIORITY,E-UTRAN_PRIORITY, THRESH_UTRAN_high, THRESH_E-UTRAN_high) andinformation related to the serving cell (e.g. GERAN_PRIORITY,THRESH_GSM_low).

NOTE 2: Throughout the specification, the phrase “neighbour cell list”will include also the E-UTRAN Neighbour Cell list where appropriate.

NOTE 3: Priorities need to be provided also for frequencies of networksthat do not support priority-based cell re-selection.

If the 3G Cell Re-selection list or the E-UTRAN Neighbour Cell listinclude frequencies of other radio access technologies, the MS shall, atleast every 5 s update the value RLA_C for the serving cell and each ofthe at least 6 strongest non serving GSM cells.

The MS shall then reselect a suitable cell of another radio accesstechnology if the criteria below are satisfied. S_non-serving_XXX is themeasurement quantity of a non-serving inter-RAT cell and XXX indicatesthe other radio access technology/mode and is defined as follows:

for a UTRAN cell, is the measured RSCP value for the cell minusUTRAN_QRXLEVMIN for the cell's frequency;

for a E-UTRAN cell, is the measured RSRP value for the cell minusE-UTRAN_QRXLEVMIN for the cell's frequency if THRESH_E-UTRAN_high_Q isnot provided; otherwise, if THRESH_E-UTRAN_high_Q is provided, is themeasured RSRQ value for the cell minus E-UTRAN_QQUALMIN for the cell'sfrequency.

For a GSM cell, S_GSM is defined as the C1 value for the cell (seesubclause 6.4);

The definition of a suitable cell is specified in 3GPP TS 25.304 forUTRAN and 3GPP TS 36.304 for E-UTRAN. However, for the purposes of cellre-selection, the suitability requirements related to signal strength(respectively signal quality) need not be evaluated (i.e. the cell maybe considered suitable even if it does not meet the requirements forsignal strength (respectively signal quality) as specified in thedefinition of suitability, using parameters obtained from the systeminformation of the candidate cell) if

either:

signal strength (respectively signal quality) was evaluated as part ofthe re-selection algorithm, and

the corresponding parameters used in the re-selection algorithm (e.g.for UMTS FDD signal quality, FDD_Qmin, FDD_Qmin_Offset; for UMTS signalstrength, UTRAN_QRXLEVMIN) were explicitly signalled in the serving cell(i.e. default values were not used)

or:

the cell meets the suitability criteria for signal strength(respectively signal quality) based on stored parameters which werereceived from a cell operating using the same radio access technologyand on the same frequency.

It should be noted and understood that the list of correspondingparameters above is not exhaustive. The disclosure applies where all, orsome specified portion, of the parameters must be explicitly signalledand not default values.

Cell re-selection to a cell of another inter-RAT frequency shall beperformed if any of the conditions below (to be evaluated in the ordershown) is satisfied:

The S_non-serving_XXX of one or more cells of a higher priorityinter-RAT frequency is greater than THRESH_XXX_high (or, in case of anE-UTRAN target, THRESH_E-UTRAN high_Q, if provided) during a timeinterval T_re-selection; in that case, the mobile station shall considerthe cells for re-selection in decreasing order of priority and, forcells of the same inter-RAT frequency or of inter-RAT frequencies ofequal priority, in decreasing order of S_non-serving_XXX, and reselectthe first cell that satisfies the conditions above;

the value of S_GSM is lower than THRESH_GSM_low for the serving cell andall measured GSM cells during a time interval T_re-selection; in thiscase, the mobile station shall consider for re-selection the inter-RATcells in the following order, and reselect the first one that satisfiesthe following criteria:

cells of a lower priority inter-RAT frequency whose S_non-serving_XXX isgreater than THRESH_XXX_low (or, in case of an E-UTRAN target,THRESH_E-UTRAN_low_Q, if provided) during a time intervalT_re-selection; these cells shall be considered in decreasing order ofpriority and, for cells of the same RAT, in decreasing order ofS_non-serving_XXX;

if no cells satisfy the criterion above, inter-RAT cells for which,during a time interval T_re-selection, S_non-serving_XXX is higher thanS_GSM for the serving cell by at least a specific hysteresis H_PRIO;these cells shall be considered in decreasing order of S_non-servingXXX.

A UTRAN FDD cell shall only be reselected if in addition to the criteriaabove, its measured Ec/No value is equal to or greater thanFDD_Qmin−FDD_Qmin_Offset.

If E-UTRAN_Qmin is provided for a E-UTRAN frequency, a E-UTRAN cell onthat frequency shall only be reselected if, in addition to the criteriaabove, its measured RSRQ value is equal to or greater than E-UTRAN_Qmin.

If THRESH_E-UTRAN_high_Q is provided for a E-UTRAN frequency, and ifE-UTRAN_RSRPmin is provided, a E-UTRAN cell on that frequency shall onlybe reselected if, in addition to the criteria above, its measured RSRPvalue is equal to or greater than E-UTRAN_RSRPmin. If E-UTRAN_RSRPmin isnot provided, the default value shall be used.

E-UTRAN cells which are included in the list of not allowed cells shallnot be considered as candidates for cell re-selection. If the strongestcells on a E-UTRAN frequency are included in the list of not allowedcells, the mobile station may reselect the strongest valid cell (seesubclause 8.4.7) on that frequency.

Cell re-selection to a cell of another radio access technology (e.g.UTRAN or E-UTRAN) shall not occur within 5 seconds after the MS hasreselected a GSM cell from an inter-RAT cell if a suitable GSM cell canbe found.

If the mobile station applies either common priorities or individualpriorities received through dedicated signalling and priorities areavailable only for some inter-RAT frequencies, cells belonging tofrequencies for which no priority is available or no threshold isprovided by the serving cell shall not be considered for measurement andfor cell re-selection.

If a mobile station in camped normally state (see 3GPP TS 43.022)applies individual priorities received through dedicated signalling andno priority is available for the serving cell, the mobile station shallconsider any GSM cell (including the serving cell) to have lowestpriority (i.e. lower than the eight network configured values).

A mobile station in camped on any cell state (see 3GPP TS 43.022) shallignore individual priorities received through dedicated signalling andshall apply priorities received from the system information of theserving cell while attempting to find a suitable cell. If the mobilestation supports CS voice services, the MS shall avoid reselectingacceptable (but not suitable) E-UTRA cells regardless of the prioritiesprovided in system information.

NOTE 4: If the MS is camping on an acceptable cell, individualpriorities are not discarded until an event leading to their deletionoccurs.

In case of a re-selection attempt towards a barred UTRAN cell, the MSshall abandon further re-selection attempts towards this UTRAN cell asdefined by the T_(barred) value on the barred UTRAN cell (see 3GPP TS25.331).

In case of a re-selection attempt towards a barred E-UTRAN cell, the MSshall abandon further re-selection attempts towards this E-UTRAN cellfor a period of up to 20 min.

In case the MS attempts re-selection to a UTRAN cell which is notsuitable (see 3GPP TS 25.304) due to being part of the “list offorbidden LAs for roaming” or belonging to a PLMN which is not indicatedas being equivalent to the registered PLMN, the MS may abandon furtherre-selection attempts towards this UTRAN cell and all other cells on thesame frequency, for a period of up to 20 min. If the MS has to performcell selection, this limitation shall be removed. If the MS isredirected under GERAN control to a frequency for which the timer isrunning, any limitation on that frequency shall be removed.

In case the MS attempts re-selection to a E-UTRAN cell which is notsuitable (see 3GPP TS 36.304) due to being part of the “list offorbidden tracking areas for roaming” (see 3GPP TS 24.301), and if theMS has received the PCID to TA Mapping information element (see 3GPP TS44.018 and 3GPP TS 44.060) for the frequency of the cell, it shallabandon further re-selection attempts towards this E-UTRAN cell and anyE-UTRAN cell which is known to belong to the same Tracking Area untilthe PCID to TA Mapping information changes in the serving cell or untilcell re-selection occurs. If the mobile station has not received thePCID to TA Mapping information element for the frequency of the cell,the MS may abandon further re-selection attempts towards this E-UTRANcell and all other cells on the same frequency, for a period of up to 20min. If the MS has to perform cell selection, this limitation shall beremoved. If the MS is redirected under GERAN control to a frequency forwhich the timer is running, any limitation on that frequency shall beremoved.

In case the MS attempts re-selection to a E-UTRAN cell which is notsuitable (see 3GPP TS 36.304) due to belonging to a PLMN which is notindicated as being equivalent to the registered PLMN, the MS may abandonfurther re-selection attempts towards this E-UTRAN cell and all othercells on the same frequency, for a period of up to 20 min. If the MS hasto perform cell selection, this limitation shall be removed. If the MSis redirected under GERAN control to a frequency for which the timer isrunning, any limitation on that frequency shall be removed.

While the present disclosure is primarily described in terms of methods,a person of ordinary skill in the art will understand that the presentdisclosure is also directed to various apparatus such as a handheldelectronic device including components for performing at least some ofthe aspects and features of the described methods, be it by way ofhardware components, software or any combination of the two, or in anyother manner. Moreover, an article of manufacture for use with theapparatus, such as a pre-recorded storage device or other similarcomputer readable medium including program instructions recordedthereon, or a computer data signal carrying computer readable programinstructions may direct an apparatus to facilitate the practice of thedescribed methods. It is understood that such apparatus, articles ofmanufacture, and computer data signals also come within the scope of thepresent disclosure.

The term “computer readable medium” as used herein means any mediumwhich can store instructions for use by or execution by a computer orother computing device including, but not limited to, a portablecomputer diskette, a hard disk drive (HDD), a random access memory(RAM), a read-only memory (ROM), an erasable programmable-read-onlymemory (EPROM) or flash memory, an optical disc such as a Compact Disc(CD), Digital Versatile Disc (DVD) or Blu-ray™ Disc, and a solid statestorage device (e.g., NAND flash or synchronous dynamic RAM (SDRAM)).

Example embodiments of the present disclosure are not limited to anyparticular operating system, system architecture, mobile devicearchitecture, server architecture, or computer programming language.

The various embodiments presented above are merely examples andvariations of the innovations described herein will be apparent topersons of ordinary skill in the art. As embodiments may be implementedin several forms without departing from the characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsscope as defined in the appended claims. Therefore, various changes andmodifications that fall within the scope of the claims, or equivalentsof such scope are therefore intended to be embraced by the appendedclaims.

It is to be noted that the methods as described have actions carried outin a particular order. However, it will be clear that the order of anyactions performed, where the context permits, can be varied and thus theordering as described herein is not intended to be limiting.

It is also to be noted that where a method has been described it is alsointended that protection is also sought for a device arranged to carryout the method and where features have been claimed independently ofeach other these may be used together with other claimed features.

Furthermore it will be noted that the apparatus described herein maycomprise a single component such as a wireless telecommunications deviceor UTRAN or other user equipment or access network components, acombination of multiple such components for example in communicationwith one another or a sub-network or full network of such components.

Embodiments have been described here in relation to 3GPP specifications.However the method and apparatus described are not intended to belimited to the specifications or the versions thereof referred to hereinbut may be applicable to future versions or other specifications.

According to an aspect of the disclosure, there may be provided a methodperformed by a device in a wireless network, the method comprising:storing a parameter of a first cell associated with a characteristic ofthe first cell; and, determining the suitability of a second cell forre-selection by the device, wherein, if the second cell has acharacteristic in common with said characteristic of the first cell,determining the re-selection suitability of the second cell inaccordance with said stored parameter.

The method may also further comprise: deleting from the device anypreviously stored parameters associated with said characteristic of thefirst cell.

The characteristic of the first cell may be the carrier frequency of thefirst cell.

According to another aspect of the disclosure, there may be provided amethod performed by a device in a wireless network, the methodcomprising: determining network identification information of said firstcell; determining a parameter of suitability criteria of a second cell;determining network identification information of said second cell; and,if said network identification information of said first cell is equalor equivalent to said network identification information of said secondcell, storing said parameter.

The method may also further comprise: after the act of storing saidparameter, associating said stored parameter with a characteristic ofthe second cell and determining the suitability of a third cell forre-selection by the device, wherein, if the third cell has acharacteristic of the third cell in common with said characteristic ofthe second cell associated with said stored parameter, determining there-selection suitability of the third cell in accordance with saidstored parameter.

The method may also further comprise: deleting from the device anypreviously stored parameters associated with said characteristic of thesecond cell.

According to another aspect of the disclosure, there may be provided amethod performed by a device in a wireless network, the methodcomprising: determining a parameter of suitability criteria of a secondcell; determining if said second cell belongs to a closed subscribergroup; and, if said second cell fails to belong to a closed subscribergroup, storing said parameter.

The method may also further comprise: after the act of storing saidparameter, associating said stored parameter with a characteristic ofthe second cell and determining the suitability of a third cell forre-selection by the device, wherein, if the third cell has acharacteristic in common with said characteristic of the second cellassociated with said stored parameter, determining the re-selectionsuitability of the third cell in accordance with said stored parameter.

The method may also further comprise: deleting from the device anypreviously stored parameters associated with said characteristic of thesecond cell.

According to another aspect of the disclosure, there may be provided adevice for use in a wireless network, the device comprising one or moreprocessors; a wireless transceiver coupled to the one or moreprocessors; and memory coupled to the one or more processors, the one ormore processors being operative to: store a parameter of a first cellassociated with a characteristic of the first cell; and, determine thesuitability of a second cell for re-selection by the device, wherein, ifthe second cell has a characteristic in common with said characteristicof the first cell, the re-selection suitability of the second cell isdetermined in accordance with said stored parameter.

The device may be further operative to: delete from the device anypreviously stored parameters associated with said characteristic of thefirst cell.

The characteristic of the first cell may also be the carrier frequencyof the first cell.

According to another aspect of the disclosure, there is provided adevice for use in a wireless network, the device comprising one or moreprocessors; a wireless transceiver coupled to the one or moreprocessors; and memory coupled to the one or more processors, the one ormore processors being operative to: communicate with a first cell;determine network identification information of said first cell;determine a parameter of suitability criteria of a second cell;determine network identification information of said second cell; and,if said network identification information of said first cell is equalto said network identification information of said second cell, storesaid parameter.

The device may be further operative to: after said parameter has beenstored, associate said stored parameter with a characteristic of thesecond cell and determine the suitability of a third cell forre-selection by the device, wherein, if the third cell has acharacteristic in common with said characteristic of the second cellassociated with said stored parameter, the re-selection suitability ofthe third cell is determined in accordance with said stored parameter.

The device may be further operative to: delete any previously storedparameters associated with said characteristic of the second cell.

According to another aspect of the disclosure, there may be provided adevice for use in a wireless network, the device comprising one or moreprocessors; a wireless transceiver coupled to the one or moreprocessors; and memory coupled to the one or more processors, the one ormore processors being operative to: communicate with a first cell;determine a parameter of suitability criteria of a second cell;determine if said second cell belongs to a closed subscriber group; and,if said second cell fails to belong to a closed subscriber group,storing said parameter.

The device may be further operative to: after said parameter has beenstored, associate said stored parameter with characteristic of thesecond cell and determine the suitability of a third cell forre-selection by the device, wherein, if the third cell hascharacteristic in common with said characteristic of the second cellassociated with said stored parameter, the re-selection suitability ofthe third cell is determined in accordance with said stored parameter.

The device may be further operative to: delete any previously storedparameters associated with said characteristic of the second cell.

According to another aspect of the disclosure, there may be provided amethod performed by a device in a wireless network, the methodcomprising: determining a parameter from a first set of criteria, saidcriteria being re-selection criteria, of a second cell and, if saidparameter satisfies a predetermined condition: determining systeminformation of said second cell; and, determining the suitability of thesecond cell for re-selection by the device using a second set ofcriteria, said second set of criteria being suitability criteria,wherein if said suitability criteria contains the parameter included insaid set of re-selection criteria, determining the suitability withoutre-determining said parameter for use in said suitability criteria.

The method may also further comprise: performing cell re-selection tosaid second cell.

According to another aspect of the disclosure, there may be provided adevice for use in a wireless network, the device comprising one or moreprocessors; a wireless transceiver coupled to the one or moreprocessors; and memory coupled to the one or more processors, the one ormore processors being operative to: determine a parameter from a firstset of criteria, said criteria being re-selection criteria, of a secondcell and, if said parameter satisfies a predetermined condition:determine system information of said second cell; and, determine thesuitability of the second cell for re-selection by the device using asecond set of criteria, said second set of criteria being suitabilitycriteria, wherein if said suitability criteria contains the parameterincluded in said set of re-selection criteria, the device beingoperative to determine the suitability without re-determining saidparameter for use in said suitability criteria.

The method according to the first aspect may also further comprise: ifthe second cell is determined to be suitable in accordance with saidstored parameter, acquiring system information of the second cell.

The method according to the first aspect may also further comprise: ifthe second cell is determined not to be suitable in accordance with saidstored parameter, omitting to acquire system information of the secondcell.

According to another aspect of the disclosure, there may be provided amethod performed by a device in a first cell of a radio access network,the method comprising evaluating an aspect of a second cell against are-selection criterion, receiving system information of said secondcell; and, determining the suitability of said second cell withoutevaluating said aspect against suitability criterion using parametersreceived in said system information.

The method may also further comprise: performing cell re-selection tosaid second cell.

According to another aspect of the disclosure, there may be provided amethod performed by a device in a first cell of a radio access network,the method comprising evaluating an aspect of a second cell against astored suitability criterion, receiving system information of saidsecond cell; and, determining the suitability of said second cellwithout evaluating said aspect against suitability criterion usingparameters received in said system information.

The method may also further comprise: performing cell re-selection tosaid second cell.

Additionally, the characteristic of the second cell may be determined byreference to one or more aspects of the physical layer, in isolation orin combination with data stored in the UE.

1. A method in a wireless cellular telecommunications device camped on aserving cell, the method comprising: storing a parameter obtained bydecoding system information of a first cell; measuring an attribute of asignal received from a candidate cell; and, evaluating the candidatecell for re-selection based on the measured attribute according to apriority-based re-selection algorithm irrespective of the storedparameter, wherein the stored parameter indicates a minimum requiredreceived signal code power.
 2. (canceled)
 3. A method according to claim1, wherein evaluating the candidate cell includes at least: acquiringsystem information of the candidate cell, the system informationincluding a candidate cell parameter; determining if the measuredattribute exceeds the candidate cell parameter by a predeterminedamount; and, if the measured attribute exceeds the candidate cellparameter by a predetermined amount, performing re-selection to thecandidate cell.
 4. A method according to claim 3 in which thepredetermined amount is 0 dB.
 5. A method according to claim 1, whereinevaluating the candidate cell for re-selection includes at least:determining if the measured attribute exceeds a predetermined defaultvalue; and, if the measured attribute fails to exceed the predetermineddefault value, determining that the candidate cell does not meetre-selection requirements.
 6. A method according to claim 1, in whichthe measured attribute is received signal code power (RSCP).
 7. A methodaccording to claim 1, in which the candidate cell is a UTRAN cell.
 8. Amethod according to claim 1, in which the serving cell is a GERAN cell.9. A method according claim 1, further comprising: measuring anattribute of a signal received from a second cell; and, evaluating thesecond cell for re-selection based on the measured attribute and thestored parameter according to a ranking algorithm.
 10. A methodaccording to claim 1, in which the serving and candidate cells are ofthe same wireless radio network.
 11. A method according to claim 1, inwhich the serving and candidate cells are of different wireless radionetworks.
 12. A wireless cellular telecommunications device adapted to:camp on a serving cell; store a parameter obtained by decoding systeminformation of a first cell; measure an attribute of a signal receivedfrom a candidate cell; and, evaluate the candidate cell for re-selectionbased on the measured attribute according to a priority-basedre-selection algorithm irrespective of the stored parameter, wherein thestored parameter indicates a minimum required signal code power. 13.(canceled)
 14. A device according to claim 12 wherein evaluating thecandidate cell includes at least: acquiring system information of thecandidate cell, the system information including a candidate cellparameter; determining if the measured attribute exceeds the candidatecell parameter by a predetermined amount; and, if the measured attributeexceeds the candidate cell parameter by a predetermined amount,performing re-selection to the candidate cell.
 15. A device according toclaim 12 in which the predetermined amount is 0 dB.
 16. A deviceaccording to claim 12 wherein evaluating the candidate cell forre-selection includes at least: determining if the measured attributeexceeds a predetermined default value; and, if the measured attributefails to exceed the predetermined default value, determining that thecandidate cell does not meet re-selection requirements.
 17. A deviceaccording to claim 12 in which the measured attribute is received signalcode power (RSCP).
 18. A device according to claim 12 in which thecandidate cell is a UTRAN cell.
 19. A device according to claim 12 inwhich the serving cell is a GERAN cell.
 20. A device according to claim12 further adapted to: measure an attribute of a signal received from asecond cell; and, evaluate the second cell for re-selection based on themeasured attribute and the stored parameter according to a rankingalgorithm.
 21. A device according to claim 12 in which the serving andcandidate cells are of the same wireless radio network.
 22. A deviceaccording to claim 12 in which the serving and candidate cells are ofdifferent wireless radio networks.
 23. A computer-readable storagemedium having stored thereon instructions which can be executed by adevice to: camp on a serving cell; store a parameter obtained bydecoding system information of a first cell; measure an attribute of asignal received from a candidate cell; and, evaluate the candidate cellfor re-selection based on the measured attribute according to apriority-based re-selection algorithm irrespective of the storedparameter, wherein, the stored parameter indicates a minimum requiredsignal code power.